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First occurrence of an Ashy-headed Green Pigeon (Treron phayrei) in Singapore

Written by Yip Jen Wei with input from the Singapore Birds Records Committee

Editing by Keita Sin, Dillen Ng, Raghav Narayanswamy, Sandra Chia, & Geraldine Lee

In October 2021 a series of national firsts made landfall in Singapore in quick succession, the first of which was a male Ashy-headed Green Pigeon Treron phayrei. But unlike most of the others, there is considerably more uncertainty to the origin of this pigeon: is it an escapee or not?

Ashy-headed Green Pigeon at Central Catchment Nature Reserve, 9 October 2021. Photo credit: Yip Jen Wei

To start off, there is little uncertainty regarding the identity of this pigeon. The bird is green, with a maroon mantle and wings, a yellow rump, yellow edges to dark flight feathers, chestnut undertail coverts, and a grey forehead. Going by the overall green colour and the fully developed maroon on wings, we can start from a male of the genus Treron, commonly known as green pigeons. Shown below is an image from the original sighting on 9 October 2021 as well as a list of Treron pigeons in Singapore and the field marks that rule them out:

Ashy-headed Green Pigeon at Central Catchment Nature Reserve, 9 October 2021. Note the maroon mantle and chestnut undertail coverts. Photo credit: Yip Jen Wei
Pink-necked Green Pigeon

T. vernans

Male has pink neck, green wings
Male Pink-necked Green Pigeon at Jelutong Tower. Photo credit: Francis Yap
Thick-billed Green Pigeon

T. curvirostra

Male has fleshy orbital ring, thick bill, and bulge to cere
Male Thick-billed Green Pigeon at Jelutong Tower. Photo credit: Francis Yap
Cinnamon-headed Green Pigeon

T. fulvicollis

Male has orange head
Male Cinnamon-headed Green Pigeon at Tampines Eco Green. Photo credit: Wong Lee Hong
Little Green Pigeon

T. olax

Male has grey head and white iris
Male Little Green Pigeon at Jelutong Tower. Photo credit: Francis Yap
Orange-breasted Green Pigeon

T. bicinctus

Male has green wings and prominent orange and pink on breast
Male Orange-breasted Green Pigeon at Udawalawe National Park, Sri Lanka. Photo credit: Avadi L Parimalam

Having ruled out all known local species we can look at species beyond our shores. Visually, the only two possible matches are Ashy-headed and Grey-fronted Green Pigeon T. affinis. To rule out Grey-fronted Green Pigeon, we can look at the clear delineation of the grey crown, as well as the orange patch on the breast which is absent in T. affinis. 

Ashy-headed Green Pigeon at Dillenia Hut. Note the orange wash to breast. Photo credit: Francis Yap

Now that we are certain of the identification, we are faced with the monumental task of figuring out its origin. Listed below are some of the factors that were considered when determining if this bird is a genuine vagrant or if it has origins in the pet trade:

    • Is this bird or related species known to migrate or travel long distances?
    • Is the species common in the pet trade, legally or illegally?
    • Is the bird in good condition?
    • Are there any similar cases of vagrancy?

First off, are Treron pigeons known to migrate or travel long distances? The short answer is that no, Treron pigeons do not typically undertake seasonal migration (Birdlife International, 2021), but pigeons are good dispersers and have been known to travel long distances in search of food. Similar species such as Thick-billed Green Pigeon have been recorded undergoing mass dispersal for fruit, along with small numbers of Yellow-vented Green Pigeon T. seimundi. In particular, night dispersal of Thick-billed Green Pigeons occur year-round, but peak in October-November (Wells, 1999)—incidentally this sighting of Ashy-headed Green Pigeon falls under the same timeframe. There are also hints of regular movement for Cinnamon-headed Green Pigeon to Pulau Ubin: in addition to sightings at other parts of the year, from 2018 to 2021 the species has been annual for the first week of December at the same fruiting trees in Western Ubin. 

Secondly we look at the prevalence of Ashy-headed Green Pigeons or other Treron species in captivity. To answer the easiest question first: no, this species is not found in Jurong Bird Park or Mandai Wildlife Reserves. In recent published surveys from Vietnam, Thailand, Singapore, and Java, Ashy-headed Green Pigeon is also not listed as a legally or illegally traded species (Chng et al, 2015; Chng & Eaton, 2016; Eaton, Leupen, & Krishnasamy 2017; Eaton, Nguyen, et al., 2017; Phassaraudomsak & Krishnasamy, 2018). However, Treron species like Pink-necked and Thick-billed Green Pigeons have been recorded in these surveys, so it is still not beyond the realm of possibility that small numbers of Ashy-headed Green Pigeons are in the black market having avoided detection.

No rings observed on the Ashy-headed Green Pigeon. Photo credit: Yip Jen Wei

Thirdly, poor condition of the bird’s plumage is often cited as an indicator that the bird was once in captivity. In this bird’s case, this is not an issue: the bird is in pristine condition, from the above image there are no rings on its legs, its nails are not clipped, and its feathers are not tattered. The physical condition of the bird offers no indication that the bird was a recent escape from captivity.

It is also helpful to compare this sighting with other cases of natural vagrancy with similar characteristics: closely related species, or species with comparable ranges and movement patterns. 

eBird range map for Ashy-headed Green Pigeon.

Here is an eBird range map for Ashy-headed Green Pigeon in the region. We can see that there are no records in Malaysia and the nearest record is in Southern Thailand, around 1200km away. 

eBird range map for Orange-breasted Green Pigeon.

The most immediately obvious comparison is Orange-breasted Green Pigeon, another vagrant Treron with similarly only one record to Singapore from 2007 (Bird Ecology Study Group, 2008). However, this species is present in Peninsular Malaysia, with the nearest record being Port Dickson, around 250km away.

Between these two cases of Ashy-headed and Orange-breasted Green Pigeon vagrancy to Singapore, both exhibit long distance dispersal, but Ashy-headed is far more extreme. We go on to see if there are any similar cases of natural vagrancy to Singapore in the range of 1200km. 

eBird range map for Hair-crested Drongo.

This is a range map for another species with only one record in Singapore: Hair-crested Drongo Dicrurus hottentottus. Distance-wise, its nearest records and even native range are comparable to Ashy-headed Green Pigeon. However, Hair-crested Drongo is a known long distance migrant (Birdlife International, 2021) while Treron pigeons are not. An Ashy-headed Green Pigeon’s natural dispersal is far more surprising than a Hair-crested Drongo’s migration to Singapore for the same distance. So while it is not accurate to compare one to the other, it does show that absence of a species in Peninsular Malaysia should not completely discount any case of potential vagrancy to Singapore. The fact that both these (and other) species have escaped detection on their journey south from Thailand along the Malaysian Peninsula is also not terribly unusual.  Given our incredibly high observer density and position at the southernmost point of Continental Asia, Singapore has a unique advantage in detecting stray vagrants, as our stellar migration season can confirm.

eBird range map for Wedge-tailed Green Pigeon.

Finally, here is a range map for Wedge-tailed Green Pigeon Treron sphenurus. Lone records in the centre and the western coast of the Indian Subcontinent represent extreme cases of just how wildly out of range Treron pigeons can sometimes show up at, with distances from the core range far exceeding our case of Ashy-headed Green Pigeon.  

These are just some examples to show that it is not inconceivable for an Ashy-headed Green Pigeon to fly 1200km from Southern Thailand to Singapore in an interesting case of natural dispersal or vagrancy. Indeed, as with the Wedge-tailed Green Pigeon, more extreme cases of Treron dispersal have occurred.

The Singapore Birds Records Committee has placed this record in Category A (natural vagrancy) through a majority vote of 6-2. To sum things up—in making this decision, the committee considered the following:

    • Ashy-headed Green Pigeon is absent from local captivity and recent surveys of traded species around the region.
    • Treron species are capable of making such long distance flights.
    • Plumage and condition of the bird offer no indication the bird is an escapee.
    • Date and location (Central Catchment Nature Reserve) of sighting are supporting factors for the bird being a genuine vagrant.
    • Lack of records in Malaysia is not unusual given Singapore’s high observer density and the fact that other species have also escaped detection to Malaysia.

Of course, unless we learn to speak Pigeonese, we will never know the true origin of this bird. This offers us some interesting food for thought—what are some indicators that would reaffirm the committee’s decision or skew it toward being an escapee?

For starters, if an Ashy-headed Green Pigeon were to turn up caged or ringed somewhere in Singapore or Malaysia where it is not known to occur, that would be definitive proof that they are traded (legally or illegally) and might swing the vote against the current decision. On the other hand, if more Ashy-headed Green Pigeons or species with similar ranges and habits were to turn up nearby, it would be much harder to discount two separate sightings as repeated incidents of escapees of a bird not known to be on the market. 

As with most national firsts of contentious origin, we may never have a definitive answer regarding the provenance of the bird, by nature of it being a national first record—there just isn’t enough information. At present, the best we can do is make an educated guess. 

References

Birdlife International. (2021). Ashy-headed Green Pigeon Treron phayrei. Birdlife Datazone. http://datazone.birdlife.org/species/factsheet/ashy-headed-green-pigeon-treron-phayrei/details

Birdlife International. (2021). Hair-crested Drongo Dicrurus hottentottus. Birdlife Datazone. http://datazone.birdlife.org/species/factsheet/hair-crested-drongo-dicrurus-hottentottus/details

Chng, S. C. L. & Eaton, J. A. (2016). In the Market for Extinction: Eastern and Central Java. TRAFFIC. Retrieved December 22, 2021, from https://www.traffic.org/site/assets/files/2393/in-the-market-for-extinction.pdf

Chng, S. C. L., Eaton, J. A., Krishnasamy, K., Shepherd, C. R., & Nijman, V. (2015). In the Market for Extinction: An inventory of Jakarta’s bird markets. TRAFFIC. Retrieved December 22, 2021, from https://www.traffic.org/site/assets/files/2466/market_for_extinction_jakarta.pdf

Eaton, J. A., Leupen, B. T. C., & Krishnasamy, K. (2017). Songsters of Singapore: An Overview of the Bird Species in Singapore Pet Shops. TRAFFIC. Retrieved December 22, 2021, from https://www.traffic.org/site/assets/files/2278/songsters-of-singapore.pdf

Eaton, J. A., Nguyen, M. D. T., Willemsen, M., Lee, J., & Chng, S. C. L. (2017). Caged in the city: An inventory of birds for sale in Ha Noi and Ho Chi Minh City, Viet Nam. TRAFFIC. Retrieved December 22, 2021, from https://www.traffic.org/site/assets/files/1580/caged-in-the-city.pdf

eBird. (2021). Ashy-headed Green Pigeon range [Screenshot]. https://ebird.org/map/pomgrp5 

eBird. (2021). Hair-crested Drongo range [Screenshot]. https://ebird.org/map/hacdro1 

eBird. (2021). Orange-breasted Green Pigeon range [Screenshot]. https://ebird.org/map/orbpig1  

eBird. (2021). Wedge-tailed Green Pigeon range [Screenshot]. https://ebird.org/map/wetpig1  

Low, A. & Cheah, W. K. J. (2008). Orange-breasted Green Pigeon sighted in Jurong. Bird Ecology Study Group. https://besgroup.org/2008/01/12/orange-breasted-green-pigeon-sighted-in-jurong/

Phassaraudomsak, M. & Krishnasamy, K. (2018). Trading Faces: A rapid assessment on the use of Facebook to trade in wildlife in Thailand. TRAFFIC. Retrieved December 22, 2021, from https://www.traffic.org/site/assets/files/11073/trading_faces_thailand_2019.pdf

Wells, D. (1999). Birds of Thai-Malay Peninsula. Academic Press.

RAP201: How to Identify Uncommon Raptors

Your handy raptor identification guide is back with a second installment – RAP201: How to Identify Uncommon Raptors! This article will cover seven species that migrate through Singapore in relatively low numbers: Grey-faced Buzzard (Butastur indicus), Common Buzzard (Buteo buteo), Eastern Buzzard (Buteo japonicus), Booted Eagle (Hieraaetus pennatus), Black Kite (Milvis migrans), Greater Spotted Eagle (Clanga clanga) and Besra (Accipiter virgatus).

Do check out RAP101: How to Identify Common Raptors to pick up tips on identifying common raptors and some background on raptor migration. As usual, we will be using the most mediocre of photos to show you do not need amazing gear for identification (though they undoubtedly come in handy for the trickier ones).

Grey-faced Buzzard (Butastur indicus)

Identifying features marked out on a Grey-faced Buzzard vs Oriental Honey Buzzard silhouette. Taken at St John’s Island, Singapore. Photo Credit: Sandra Chia

The Grey-faced Buzzard is a medium-sized migratory raptor. It has longer, slimmer wings than the Oriental Honey Buzzard (Pernis ptilorhynchus) when fully extended, with a white throat and dark mesial stripe. It also has five ‘fingers’ as opposed to the Oriental Honey Buzzard’s six ‘fingers’. In juveniles, that are similar in shape to adults, the mesial stripe are not as pronounced and they have streaks on their underparts instead of barrings.

Buzzards sp. (Buteo sp.)

Identifying features marked out on pictures of a Common Buzzard vs Eastern Buzzard vs Grey-faced Buzzard. Taken in Singapore. Photo Credit: Keita Sin

Buteo sp. refers to buzzards, that are stocky, medium-sized raptors with long wings ending in five ‘fingers’. They can be differentiated from Grey-faced Buzzards, which also have five ‘fingers’, by the lack of a mesial stripe, shorter tail, shorter and more rounded wings. Taxonomy of the Buzzards are contentious, with different ornithological authorities treating them differently – some consider the Common and Eastern Buzzards separate species while some recognize them as subspecies (Gill et al., 2021; Billerman et al., 2020; McClure et al., 2020). Common Buzzards (Buteo buteo) are browner overall compared to Eastern Buzzards (Buteo japonicus). Given the messy taxonomy it is currently unclear where exactly the Eastern Buzzards in Singapore arrive from.

Identifying features marked out on pictures of Booted Eagle vs Black Kite vs Oriental Honey Buzzard vs juvenile Brahminy Kite. Taken in Singapore. Photo Credit: Sandra Chia (Booted Eagle and Oriental Honey Buzzard), Keita Sin (Black Kite) and Yip Jen Wei (Brahminy Kite).

Booted Eagle (Hieraaetus pennatus)

The Booted Eagle has wings that are somewhat similar in shape to the locally common Brahminy Kites, with six ‘fingers’. It has pale shoulder spots on the upperwing, resembling ‘headlights’. Compared to the Oriental Honey Buzzard that also has six ‘fingers’, the Booted Eagle has a more compact, stockier giss and a squarish tail. The Booted Eagle can also be differentiated from juvenile Brahminy Kites and Black Kites by their lack of distinct ‘M’ shape in the wings and lack of white primary patches. This species has two morphs – dark and pale, and more information can be found on our species page.

Black Kite (Milvus migrans)

The Black Kite also has six ‘fingers’, but differs from the Brahminy Kite, Oriental Honey Buzzard and Booted Eagle by having a distinctly forked tail. It can also be told from Oriental Honey Buzzard and Booted Eagle by distinct ‘M’ shape in flight, resembling Brahminy Kites. However, the white wing patches in the Black Kite are restricted to the base of their primaries unlike juvenile Brahminy Kites that have a larger patch of white.

Greater Spotted Eagle (Clanga clanga)

Identifying features marked out on a Greater Spotted Eagle vs Changeable Hawk Eagle. Taken in Singapore. Photo Credit: Sandra Chia

The Greater Spotted Eagle has an overall dark plumage, with broad wings ending in seven ‘fingers’. It can be told apart from the Changeable Hawk Eagle by less rounded wings, resulting in less of an ‘armpit’ and the presence of a light vent. It is also much bigger. It also has white fringing on underwing coverts, with a whitish patch at base of outer primaries. More information on this can be found on our species page.

Besra (Accipiter virgatus)

Identifying features marked out on pictures of a Besra vs Japanese Sparrowhawk vs Shikra. Taken in Singapore. Photo Credit: Keita Sin (Besra and Shikra from Thailand) and Sandra Chia (Japanese Sparrowhawk).

The Besra is a sparrowhawk (typically referred to by their genus name Accipiter), and is hence small and closer in size to Japanese and Chinese Sparrowhawks. Like the Japanese Sparrowhawk and Shikra (also an accipiter – a very rare bird with only two local records), it has five ‘fingers’ but differs by having a strong mesial stripe, with its tail showing alternating dark and light tail bands of equal width. The Japanese Sparrowhawk in comparison typically has wider white bands, while the Shikra can be told apart by their much longer looking tail. The Besra has only been recorded in Singapore a handful of times, making it quite the rarity.

We hope this has been useful in telling these uncommon raptors apart. As some species can be rather tricky to identify, do check in with helpful birders on social media and identification forums when in doubt!

Not to worry, we have not forgotten about the Harriers. Keep your eyes peeled for the next installment, where we will dive into identification of Harrier species that migrate through Singapore!

Acknowledgements

Thanks to the field buddies, especially Max Khoo, Low Bing Wen and Oliver Tan, for suggesting a sequel covering uncommon raptors be done up and the team for their comments on the article.

References

Billerman, S. M., Keeney, B. K., Rodewald, P. G., & Schulenberg, T. S. (Eds.). (2020). Birds of the World. Ithaca, NY, USA: Cornell Laboratory of Ornithology.

DeCandido R., Nualsri C., Siponen, M., Sutasha, K., Pierce A., Murray, J. & Round, P. D. (2014). Flight identification and plumage descriptions of six Accipiter species on southbound migration at Khao Dinsor, Chumpon province, Thailand. BirdingASIA, 21(2014), 52-62. Link: https://www.researchgate.net/publication/303712756_Flight_identification_and_plumage_descriptions_of_six_Accipiter_species_on_southbound_migration_at_Khao_Dinsor_Chumphon_province_Thailand

del Hoyo, J., Collar, N., Marks, J. S. & Kirwan, G. M. (2020). Eastern Buzzard (Buteo japonicus), version 1.0. In del Hoyo, J., Elliott, A., Sargatal, J., Christie, D. A., & de Juana, E. (Eds). Birds of the World. Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bow.combuz6.01

Eaton, J. A., Balen, B., Brickle, N. W. & Rheindt, F. E. (2021). Birds of the Indonesian archipelago, Greater Sundas and Wallacea. Lynx Editions.

Gill, F., Donsker, D., & Rasmussen, P. (Eds). (2021). IOC World Bird List (v11.2). Link: https://www.worldbirdnames.org/new/ 

Lindhom, A. & Forsten A. (2013). “Common”  Buzzards of South China and South-East Asia. Caluta, 4, 1-11. Link: http://www.caluta.liitin.net/Caluta/caluta4.html

McClure C. J. W., Lepage D., Dunn L., Anderson D. L., Schulwitz S. E., Camacho L., Robinson B. W., Les Christidis, Schulenberg T. S., Iliff M. J., Rasmussen P. C. & Johnson J. (2020). Towards reconciliation of the four world bird lists: hotspots of disagreement in taxonomy of raptors. Proc. R. Soc. B, 287. Link: https://royalsocietypublishing.org/doi/pdf/10.1098/rspb.2020.0683

Robson, C. (2008). A Field Guide to the Birds of South-East Asia. New Holland Publishers.

Singapore Birds Database: A Digital Museum of Local Bird Information

~Record keeping with the future in mind~

By Sin Yong Chee Keita & Dillen Ng

Summary

  • The Singapore Birds Database contains an easy-to-use search interface that allows you to look up information on locally rare bird species
  • More than 1000 records across over 160 species are now freely available to the public
  • You can contribute to our project by completing this simple form if you encounter any rare birds
  • Feel free to contact us via the Singapore Birds Project regarding any feedback or suggestions
  • If you need help with identification,  don’t hesitate to ask on our Facebook group where many regionally experienced birdwatchers are present
  • To find out more about our philosophy and objectives of this database, check out this write-up

Basic questions but who has the answers?

A Digital Museum. Quite a catchy name, isn’t it? Now that we have grabbed your attention, here are some simple questions that we want to ask you: How many times has the Fairy Pitta been recorded in Singapore? The answer is twice. Easy, right! It’s been all over the news recently. Okay then, what about Chinese Blue Flycatcher? Hmm, there were some recent records but it’s difficult to be certain of the total count. Two? Three? The answer is four. Well, what about the Northern Boobook? Now that’s a tough one. Does anyone have this information at their fingertips…? A rather basic piece of information, it seems—just how many times a species has been seen. Yet no one appears to have the answer.

From left: Fairy Pitta Pitta nympha, Chinese Blue Flycatcher Cyornis glaucicomans, and Northern Boobook Ninox japonica. Photos by Dillen Ng and Sin Yong Chee Keita.

To find out more, let’s check what Singapore Birds Project has to say about the Northern Boobook.

Local Status: Uncommon migrant

Location: Records from Tuas South, Pasir Ris Park, and Satay by the Bay but could conceivably occur in any place with trees. 

This gives us some rough ideas about the species. It certainly is not a common bird, so maybe less than 20 records in total? Still we’d like to know more details. After all, it is still a highly sought after species—knowing where and when to look for it provides clues on the best way to find an individual.

Searching eBird is not particularly effective either. There are a large number of data points with some being repeats of the same sighting, and it would be too time consuming to click through every point on the map.

Map of Northern Boobook sightings on eBird

Finding the answer to this seemingly simple question is actually rather difficult. One would first need to make an excel spreadsheet, click through every eBird data point, then collapse possibly duplicated sightings…and that’s not all. To obtain pre-eBird era information, there would also be a need to flip through old literature to tabulate all records.

This used to be the convoluted journey that any curious birdwatcher had to take to learn about most species, but that will no longer be the case.

Introducing the Singapore Birds Database

Using our newly launched Singapore Birds Database, you can get your answer in just a few clicks. All you need to do is to search for a species name, and voila! We can see that there are at least 16 confirmed local records of the Northern Boobook. How easy is that?!

The Singapore Birds Database contains local records of over 160 species of rare birds. Not only are details on the dates, location and species name of sightings included, we also provide links to primary sources (if available online) such as Facebook or scientific publications so that anybody can verify the data for themselves. For cases where there are records of a rarity at the same (or nearby) location after a period of absence, if we think that multiple records refer to the same individual, we provide internal links so that users can cross-reference the records.

A search of Northern Boobook in the Singapore Birds Database

How the Singapore Birds Database was conceptualised

In 2019/2020, we had a tremendous migration season with vagrants such as a Fairy Pitta, Daurian Redstarts, and Taiga Flycatchers showing up. It was quite extraordinary and we worked to publish about its peculiarity together with Singapore’s eBird reviewer, Martin Kennewell. Researching for our paper was very challenging because basic information about a species in Singapore (e.g. how many times has it been seen) was not readily available.

We thought to ourselves, why not create a database to address this problem? In January 2020, we decided to embark on a massive project to compile all records of significant bird species in Singapore. And let’s not just compile it for personal use. Let’s make it public. Let’s make it comprehensive. Let’s make it easy to use. Let’s make sure that it is regularly updated. Let’s make it free to use. And most importantly, let’s make it transparent. We aim for this database to provide records, substantiated with primary evidence, such that users can also question and independently arrive at answers themselves.

We reviewed over 1000 records manually by checking through every available primary source, visiting libraries countless times, and trawling through the web like crazy. After 1.5 years of effort, we are finally ready to launch this database via the Singapore Birds Project website. For those who are keen, you can find out more about the processes and philosophy of our work in this write-up.

How can you be a part of our project?

  1. If you encounter any rare species, please submit your sighting at this link to play a part in documenting Singapore’s avifauna. We also strongly encourage you to make use of eBird for your day-to-day birding adventures.
  2. Please let us know if you notice any errors! We will do our best to update the database as soon as possible and with proper acknowledgements.
  3. Lastly, if you have any ideas for our database or the Singapore Birds Project, feel free to contact us!

Moving forward

All records submitted to our database will be reviewed by the Singapore Birds Project Record Committee. One key focus behind our integrated user submission system and database is transparency, because we believe in making all records and decisions publicly accessible. Given that sightings are shared across a variety of online platforms nowadays, we will continue to actively look out for records of rarities to prevent data from slipping through the cracks, while encouraging user submissions. We aim to cover all bases by being vigilant and using a future ready approach.

The birdwatching community in Singapore has been growing rapidly and everyone is yearning to learn more about our feathered friends. The Singapore Birds Project has filled in the niche for being a reliable source of updated and accurate bird information. This new database is a big step forward in our aim to contribute to the local community. We aim to update our database with more information and explore various avenues to utilise this data. We hope to continue doing our work, not alone, but as a community together with all of you.

Acknowledgements

Raghav Narayanswamy and Francis Yap: A massive thank you to the two of you for creating the digital platform to present our database in such an elegant manner. If not for your efforts, our work would have been constrained to a single excel spreadsheet.

Adrian Silas Tay, Goh Cheng Teng, Lester Tan, Martin Kennewell, Richard White, and See Toh Yew Wai: The feedback all of you provided when testing the initial stages of our database helped improve our public interface tremendously.

Elize Ng, Geraldine Lee, Movin Nyanasengeran, Sandra Chia, Tan Hui Zhen, Twang Fang Qi: Your reviews helped to greatly refine our overarching document that explains the processes behind our work. Thanks for your time in reading through 18 pages of texts. We will probably continue sending you all our future blog posts, so be prepared :p

Martin Kennewell: We are constantly blown away by how you take on the herculean task of curating Singapore’s eBird data with such precision. Your efforts over the past few years in promoting the use of this platform locally is finally paying dividends. Thank you so much for your work!

Bird Ecology Study Group, Lee Kong Chian Natural History Museum, Nature Society (Singapore) Bird Group, Oriental Bird Club: Efforts and publications by these organisations have served as key documentation for numerous historical records, to which we are grateful for.

The past and present administrators of key Facebook groups (Bird Sightings, Birder’s Group, Singapore Birders): Curating content on Facebook is not easy [I know, because I’ve recently become one of them! – Keita] and the efforts have allowed us to search for important information when compiling modern records. Thank you for your effort.

Every single person who has contributed to advancing the local ornithology scene over the past two centuries: Thank you, if not for the efforts of everybody who documented and shared their records, we would be living in a very different community today.

PIPIT101: Identifying Singapore’s First Tree Pipit Anthus trivialis

Written by Richard White, infographic by Keita Sin
Editing by Martin Kennewell, Keita Sin, Sandra Chia, & Dillen Ng

The birding community was presented with an identification challenge today with the arrival of a vagrant pipit species. These small, brown, streaky birds can be difficult to identify at the best of times. An unfamiliar, out of context, vagrant can be a real headache. So how to start the identification process? These notes might help.

Worldwide, there are about 40 species of pipit, mostly in the genus Anthus. Within Southeast Asia nine species are regular; in Singapore Paddyfield Pipit A. rufulus is a resident breeder, Red-throated Pipit A. cervinus is an annual non-breeding visitor in small numbers and Olive-backed Pipit A. hodgsoni is a rare vagrant with only one record at Bidadari in December 2010.

A bird discovered in a small suburban park in Clementi, Singapore, on 23 October 2021 by Soh Kok Choong was initially misidentified as a Eurasian Skylark Alauda arvensis. This species is a rare vagrant to Singapore with one previous record at Pandan Reservoir in November 2018. Jan Jaap Brinkman saw the post on 25 October, realized it was not a Eurasian Skylark but more likely to be a Tree Pipit A. trivialis (a first record for Singapore), and alerted the birding community. It was relocated quickly on 25 October and the identification of Tree Pipit confirmed.

But how do we know it is a Tree Pipit? Ideally, it would have been heard to call. While pipits tend to look alike (variations on brown and streaky), their calls are helpful and in most cases distinctive. Calls are notoriously hard to describe, which is why I am going to direct you to resources such as Xeno-canto should you wish to learn more about pipit calls. Unfortunately, this bird was either silent or could not be heard to call over the traffic on Clementi Road.

Faced with a silent pipit, how do we make an identification? First, let’s discount the commoner options (without spending time here on why it is not a Eurasian Skylark).

Of the three pipit species previously recorded in Singapore, Paddyfield Pipit is the commonest and therefore most likely pipit to be encountered. It is one of the larger pipits, >16 cm long and has a longer-legged and more upright appearance than the other pipits which are smaller and more horizontal in their stance. Size has to be used carefully, since the smaller pipit are merely < 16 cm long. Without being very familiar with pipits, this marginal size difference in a lone vagrant individual may not be helpful. The other feature that points away from Paddyfield Pipit is the extensive streaking across the breast of this bird, more than would be found on a Paddyfield Pipit. This combined with the short-legged, more horizontal gait, indicate that this pipit is not a Paddyfield.

Red-throated Pipit is the next most likely option. Smaller, with a more horizontal gait, this species is similar to a Tree Pipit in non-breeding plumage. However, the streaking on the breast typically extends strongly onto the flanks which this bird does not have. The upperparts are usually more boldly streaked to the rump as well, again lacking in this bird. Red-throated Pipit also typically has strong off-white mantle braces. These pale lines can be seen on this bird, but are not as well marked as would be expected on a Red-throated Pipit. The plumage tones of this bird give an impression of warm buff/browns in tone, while Red-throated Pipit should be colder grey/browns. So it appears the bird is not a Red-throated Pipit and therefore a real rarity.

Olive-backed Pipit is the only other pipit species to be recorded in Singapore. As the name suggests, the upperparts of this species should give an impression of olive/brown, which is not seen on this individual. Olive-backed Pipit typically also shows a strongly marked head and face pattern, with a clear supercilium above the eye and a well marked spot at the rear of the ear coverts. Lacking these features, this bird is not an Olive-backed Pipit either.

Now into the territory of a national first, the list of possibilities opens up. Within the region, Rosy Pipit A. roseatus would be more boldly marked, and Buff-bellied Pipit A. japonicus lacks the warm plumage tones of this bird. It is not one of the larger pipits (Richard’s A. richardii, Blyth’s A. blythi or Long-billed A. similis). We are left with Tree Pipit or maybe something even more extreme from outwith the region, such as a Pechora Pipit A. gustavi or Meadow Pipit A. pratensis.

Pechora Pipit is easily discounted since it shows a distinct primary projection beyond the longest tertial, which this bird does not show.

Meadow Pipit, typically a short distance migrant, is an outside chance from much further west. Though this makes it less expected, it should be considered. It is superfically very similar to Tree Pipit, but typically shows a clustered spot of streaking in the centre of the breast not shown by this bird. It is also less likely to perch in trees as this bird did often. The call is different but this silent bird does not help us. Finally and conclusively, scrutiny of digital images shows this bird has a short hind claw – shorter than would be seen on a Meadow Pipit.

Our lone, silent, pipit can be confidently identified as a Tree Pipit based on the plumage and structural features, as well as the behaviour and gait (jizz):

  1. Underparts: Well marked narrow black streaks across the chest/breast on a warm buff base. Streaks do not extend strongly onto the flanks
  2. Upperparts: warm buff/brown, with dark centred feathers giving a well marked, but not strongly contrasting, appearance. A well marked row of median primary coverts were slightly darker centred and paler fringed than surrounding feathers, producing a clear (but not bold) wing bar.
  3. General behaviour: spent most time walking through long grass foraging for invertebrates with a horizontal gait and occasionally giving gentle tail pumps (which is also a feature of Olive-backed Pipit). Flew with a strong bounding flight into mid-canopy of trees where it would perch, rest and preen before returning to feeding on the ground.
Key identification features of the Paddyfield, Red-throated, Olive-backed and Tree Pipit. Photo and infographic: Keita Sin
eBird screenshot of the Tree Pipit, taken 25 October 2021. It can be seen that this species is a long-distance migrant that winters in Africa and India.
eBird screenshot of the Meadow Pipit, taken 25 October 2021. This species is typically a short distance migrant, distributed further west than the Tree Pipit. It is therefore less expected for this species to arrive in Singapore.

Further notes:
1) Edited 26 October 2021: The upperparts description previously read “A well marked row of greater primary coverts … …”. This has been corrected to “row of median primary coverts … …”.
2) After the release of our article, Siti Soedarsono shared with us that she photographed the bird earlier at the same site on 19 October 2021. This date serves as the new first date for this record. We thank Siti for graciously sharing the information.

RAP101: How to Identify Common Raptors

The peak of Singapore’s raptor migration will soon be upon us. From October to December, large numbers of migratory raptors will pass through Singapore, as they move from their breeding grounds in temperate northeast Asia to tropical southeast Asia (Bildstein, 2006). This constitutes autumn migration, where birds migrate southwards to avoid frigid winters in their home grounds. Around March to May, the birds will head back north to breed, but fewer species seem to pass through Singapore and in smaller numbers. Different species of raptors have been observed to peak in their passage through Singapore in different months.

During this period, you’ll find birders heading to popular raptor watching spots such as Henderson Waves, Telok Blangah Hill Park and Tuas to try their luck at snagging rarer ticks, or to enjoy viewing the large number of raptors migrating overhead. At the same time, you’ll find posts popping up on local Facebook pages requesting for raptor identification. While raptor plates in field guides are handy for identification, good guides can be costly and those short on cash or new to the hobby may not be keen on making such purchases yet. Even so, while guides have detailed illustrations of the raptors in full colour with all identification features clearly indicated, migrating raptors often thermal high in the sky and our grainy, backlit pictures may look like this:

Large flock of migratory raptors at Henderson Waves, Singapore. Photo Credit: Sandra Chia

So how do we tell what’s what?

Equipped with my trusty but outdated Nikon 300mm F4 (no teleconverter!), my photos of migrating raptors may be the worst of the lot. Thankfully, you do not need amazing photos to identify the dots passing overhead. This article will feature five common raptors: Changeable Hawk Eagle (Nisaetus cirrhatus), Crested Honey Buzzard (Pernis ptilorhynchus), Chinese Sparrowhawk (Accipiter soloensis), Japanese Sparrowhawk (Accipiter gularis) and Black Baza (Aviceda leuphotes), and we’ll go through some general pointers on how to differentiate what’s what.

Changeable Hawk Eagle (Nisaetus cirrhatus)

Identifying features marked out on a Changeable Hawk Eagle silhouette. Taken at Henderson Waves, Singapore. Photo Credit: Sandra Chia

The Changeable Hawk Eagle is a medium sized raptor with seven ‘fingers’. Some individuals undergoing moult may have less than seven ‘fingers’, but can still be differentiated by its round wings, which result in a silhouette with pronounced ‘armpits’. This species can come in a dark or pale morph. This is an uncommon resident species that may often be seen while observing migratory raptors.

Crested Honey Buzzard (Pernis ptilorhynchus)

Identifying features marked out on a Crested Honey Buzzard silhouette. Taken at Henderson Waves, Singapore. Photo Credit: Sandra Chia

The Crested Honey Buzzard is another medium sized raptor with six ‘fingers’. The migratory subspecies, Pernis ptilorhynchus orientalis, is commonly referred to as Oriental Honey Buzzard. If moulting, individuals may also have fewer than six ‘fingers’. It can be differentiated from other medium sized raptors by its relatively small head and less rounded wings. The Crested Honey Buzzard also comes in various morphs such as light, dark, and an array of intermediate morphs (DeCandido et al., 2015). If you would like to take a deep dive into Crested Honey Buzzard identification, you can check out DeCandido et al. (2015).

Chinese Sparrowhawk (Accipiter soloensis)

Identifying features marked out on a Chinese Sparrowhawk silhouette. Taken at Henderson Waves, Singapore. Photo Credit: Sandra Chia

The Chinese Sparrowhawk is an Accipiter, a globally distributed genus typically known as hawks.  Accipiters are generally smaller than the two raptors discussed above, resulting in a very different general impression of their size and shape. This species has four ‘fingers’, tipped black. More information on how to identify males, females and juveniles of the species can be found on our species page here.

Japanese Sparrowhawk (Accipiter gularis)

Identifying features marked out on a Japanese Sparrowhawk silhouette. Taken at Henderson Waves, Singapore. Photo Credit: Sandra Chia

The Japanese Sparrowhawk is of similar size to the Chinese Sparrowhawk but can be told apart as it has five ‘fingers’ instead of four. More information on identification of males, females and juveniles can also be found on the species page, here. More information on telling apart Accipiter species can be found in DeCandido et al. (2014).

Black Baza (Aviceda leuphotes)

Identifying features marked out on a Black Baza silhouette. Taken at Henderson Waves, Singapore. Photo Credit: Sandra Chia

The Black Baza is of similar size to the sparrowhawks discussed above but differs by its wing shape, which is more rounded than that of the sparrowhawks, resembling paddles. It is also distinctly coloured, with a prominent band of white across the upper breast and thinner black, white, and chestnut stripes across the lower breast and belly. This species is mostly seen from late November onwards (eBird, n.d.).

We hope this article has served as a useful crash course on identification of common raptors we might encounter while raptoring in the coming months. Leave a comment below if you’d like us to cover other species!

Happy raptoring and hope to see everyone’s lists on eBird!

Acknowledgements

Thanks to Jin Rong and the team (Dillen, Francis, Keita, Movin and Raghav) for their comments on the article and to the experienced birders who taught me how to identify raptors over the years.

References

Bildstein, K. L. (2006). Migrating raptors of the world: their ecology & conservation. Cornell University Press.

DeCandido R., Nualsri C., Siponen, M., Sutasha, K., Pierce A., Murray, J. & Round, P. D. (2014). Flight identification and plumage descriptions of six Accipiter species on southbound migration at Khao Dinsor, Chumpon province, Thailand. BirdingASIA, 21(2014), 52-62. Link: https://www.researchgate.net/publication/303712756_Flight_identification_and_plumage_descriptions_of_six_Accipiter_species_on_southbound_migration_at_Khao_Dinsor_Chumphon_province_Thailand

DeCandido, R., Siponen, M., Smit, H., Pierce, A. & Allen, D. (2015). Flight identification and migration pattern of the Oriental Honey Buzzard Pernis ptilorhynchus orientalis in southern Thailand, 2007-2014. BirdingASIA, 23(2015), 27-33. Link: https://www.theflywayfoundation.or.th/download/Oriental%20Honey%20Buzzard%20in%20southern%20Thailand%202007%E2%80%932014.pdf

eBird. (n.d.). Black Baza. https://ebird.org/species/blabaz1/SG

Singapore Avifauna records on eBird

Five of the 27,000+ records uploaded to eBird from the old Singapore Avifauna newsletters. Photos taken in Singapore and elsewhere (credit: Raghav Narayanswamy and Keita Sin).

For much of my first few years of birding in Singapore, I wondered how the data from earlier eras in local ornithology could be made available for more to benefit; if early dates and late dates, major hotspots, past trends in the local avifauna, among other useful information, could be compiled in an accessible format for the community at large. After all, this small country has always been blessed with a higher-than-average observer coverage relative to its surrounding regions. The data could fill major gaps in understanding Asian avifauna, and be greatly beneficial to interested local birdwatchers as well.

So when I first saw that the Nature Society (Singapore) (NSS) had made its old editions of Singapore Avifauna from 1987 through 2010 available on its website, it was immediately clear that this could be a great resource for the birding community in Singapore if it could be consolidated into a more readily-accessible format. To really know how many times a species has been recorded locally, or which months it appears most frequently, manually scrolling through hundreds of reports for that species would not be practical. Rather, the data would need to be in a spreadsheet, and easily searchable, for the information to be most useful.

Recently, as Keita discussed last week, eBird has established itself as the most widely-used citizen science database for avian records. Many studies have referenced data stored in eBird to examine trends and achieve important conservation outcomes. It also reached a major milestone — 1 billion bird observations — in May this year, reinforcing its position as a powerful tool for conservationists and casual birders alike to share observations and further broaden our collective knowledge. It was clear to me that putting these important records from SINAV on eBird was the best way to make them as impactful as they can possibly be.

In collaboration with Singapore’s eBird reviewer Martin Kennewell, after obtaining permission from NSS to consolidate and upload the records, I set to work on designing a program to extract species names, observation counts, dates, and locations, as well as observer names for proper credit, for all the volumes of Singapore Avifauna available on the NSS website. Dividing this process into two steps: conversion of the PDFs (stored as images) into text, followed by extracting the important details from the text, I was able to upload over 27,000 individual observations, around 23,000 from Singapore and 4,000 from Malaysia and Indonesia.

The records uploaded now make up around 75% of all eBird records until 1990, and over 25% of all records until 2010 (the last year that Singapore Avifauna was published).

I can’t say that this journey was always smooth; one of the biggest challenges I faced was resolving old locations, with old place names, to current landmarks or points on the map which could be uploaded to eBird. With Martin’s expertise and support, I was able to resolve most of these, and sent a further few to NSS for their review. Additionally, some older editions of SINAV were missing; indeed, this was an era with limited technological access and keeping track of documents was admittedly more challenging than it has become today. Older records also suffered from a lack of specific counts; especially as birds that have now become rare once numbered in the dozens or even hundreds, observers sometimes may not have made the effort to accurately count these species.

See, for example, the entry for Sanderling in the report for February 1987.

This species is now barely an annual visitor; in the 80s, 90s, and even the early 21st century, counts in the double digits were regular. It’s hard to believe this count of 100 Sanderlings along with exceptional counts of other shorebirds, was just over 15 years ago.

A mixed flock of shorebirds in Thailand from 2019. Such scenes are now nothing more than a distant dream in Singapore today.
A mixed flock of shorebirds in Thailand from 2019. Such scenes are now nothing more than a distant dream in Singapore today.

Sometimes the work was tiring and it became difficult to continue, but I always knew the reward of making all these sightings accessible was worth the effort. In the end, after probably 100 hours of work, I uploaded the data to the NSS Records eBird account.

An example

The excerpts below are from Volume 19 (Jan-Mar) of Singapore Avifauna, published in 2005 (link). I’ve used this example to highlight how the process of digitizing reports into individual records works. For January, February, and March of 2005, Blue-crowned Hanging-Parrots were recorded a total of 12 times. Since the report is split into each of the months, this species appears three times.

These three entries are then converted into text with optical character recognition and combined into one overall entry for the period covered by the report, in this case January to March:

BLUE-CROWNED HANGING-PARROT Loriculus galgulus
1 over Dairy Farm Road, 17/1 (LKS) and 18/1 (LKS) and 4 at Malcolm Park, 30/1 (NK/LKS/FR/IR/JR). At Botanic Gardens, 7 were counted on 4/2 (LKS) and 5 on 28/2 (AF/LKS). Also 3 over Nee Soon, 8/2 (LKS), 1 at MacRitchie Reservoir, 16/2 (LKS) and 28/2 (AF/LKS), and 1 over Dairy Farm Road, 24/2 (LKS). 1 heard at the foot of Bukit Timah, 12/3 (LKS), 1 flying over Dairy Farm Road, 22/3 (LKS) and 3 at Sime Road, 27/3 (LKS).

The individual records are then separated by looking for “sets” comprising the four important pieces of information for each record: count, date, location, and observer names. Of these, the most challenging to parse out is the location. In this case, there’s no extraneous information that we need to ignore, so it seems relatively straightforward to just use the leftover text as the location. But sometimes, sightings are associated with lengthy descriptions and the location needs to be extracted from that description – so I had to use natural language processing to pick out the location.

For the example above, the following 12 sightings would then be uploaded to eBird. This checklist shows how the first record (17 Jan) would appear in eBird’s outputs.

This project is mostly complete, and with it, thousands of bird observations recording hundreds of species have now been placed somewhere they can be accessed by researchers and amateurs alike. As more people come forward to contribute their sightings and share their knowledge, we can make more meaningful progress in conserving our valuable local wildlife.

Acknowledgements

This piece was written with the help of comments and advice from the Singapore Birds Project team (Dillen, Francis, Keita, Movin, and Sandra). My project drew on over a hundred reports made available by NSS on its website; their permission for me to take on this project also made this project possible. I also appreciate Martin’s contribution to many aspects of my project, including location-matching and manual approval/rejection of the uploaded records.

References

Sullivan, B. L., Aycrigg, J. L., Barry, J. H., Bonney, R. E., Bruns, N., Cooper, C. B., … Kelling, S. (2014). The eBird enterprise: An integrated approach to development and application of citizen science. Biological Conservation, 169, 31–40. doi:10.1016/j.biocon.2013.11.003

Sullivan, B. L., Wood, C. L., Iliff, M. J., Bonney, R. E., Fink, D., & Kelling, S. (2009). eBird: A citizen-based bird observation network in the biological sciences. Biological Conservation, 142(10), 2282–2292. https://doi.org/10.1016/j.biocon.2009.05.006

Why you should start using eBird!

Imagine a world where you could predict the arrival of your favourite migratory bird, get immediate identification help for an unfamiliar bird, and contribute to science and conservation just by being out in the field. I have some fantastic news for you…that’s the world we live in now!

BirdCast is a forecast map that utilises weather forecast maps to model bird migration. Scientists from the Cornell Lab of Ornithology are able to track data on how birds travel, allowing myriads of research ranging from the effects of climate change, to single events such as the influences of hurricanes on bird movements to be projected. One of the key components that makes BirdCast functional is data from eBird. The most rudimentary form of data – actual bird encounters from the birdwatchers in the field – are combined with highly intricate weather surveillance infrastructure, to make fairly accurate predictions of bird migration. A well-known example of how eBird data has transformed the birding experience of beginners is the Merlin platform which uses Artificial Intelligence (AI) to identify birds. Users simply need to upload a photograph or sound recording of the bird and the AI will suggest several potential candidates. This complex AI did not magically appear, though – it was made possible through feeding tons of photographs and sound recordings to the computing system, once again with the help of eBird data. These platforms allow birding to be much more targeted, focused, and friendly, both for beginners and the most hardcore of birdwatchers. Sounds great, doesn’t it? Now here’s the catch: at present, BirdCast is only available in the United States. The platform was first launched in 2018, and research is still concentrated in the area where eBird data is most abundant. On the other hand, although Merlin started out being only available in United States initially, there is now a package for Singapore, though it still struggles with similar looking birds such as Phylloscopus warblers. With enough contribution from the regional birding community, other platforms such as BirdCast will hopefully be made available to us as well. A massive way you could contribute to improving the precision of these tools is by contributing to eBird.

eBird is a citizen-science platform that was first launched over 10 years ago (Sullivan et al., 2009) and anybody is able to create an account for free. Through the platform, bird sighting information, along with their photographs and sound recordings, can be uploaded. A highly user-friendly mobile phone application is available and all you need to do when you are out birding is to start a list, select a location, and just tap a button that corresponds to a species you encounter in the field. Detailed information such as sex, behaviour, and other observations can be optionally added. A web platform is also available where you can later upload the photographs and sound recordings you took.

A simple example of how the eBird mobile app works. All you need to do is tap some simple buttons!

In your eBird account, not only will you be able to check your daily sightings, but you can also track your birding statistics by generating monthly or yearly summaries. Furthermore, there is a particular function that you would definitely love as a birder – the needs and rarities alert. These alerts will send you emails when other eBirders find a bird that you need (i.e. not recorded in your eBird account) or are locally significant. In these alerts, you can even set multiple filters to suit your needs: for example, if you have seen a Fairy Pitta Pitta nympha elsewhere before, you might not necessarily find the need to see one in Singapore so you can filter it out from your personalised eBird alert list. On the other hand, if you are doing a big year, you might want to search for relatively common birds such as the Dark-sided Flycatcher Muscicapa sibirica the moment one is locally seen.

The eBird settings page where you can subscribe to your preferred alerts.

Some might have reservations regarding immediate sharing of sightings – certain sites such as housing estates might be sensitive, or some birds might be nesting when you find them. In such cases, you can also upload your data post-hoc through an easily formattable excel sheet once you are comfortable with making the data public. Likewise, if you prefer to be private, there are options to upload your sightings anonymously or hide your lists (you will still need an account, but your name/list will not be displayed publicly). Additionally, concerns about the dangers of publicising locations for species such as the Critically Endangered Straw-headed Bulbul Pycnonotus zeylanicus due to the presence of poaching activities can be eased: there is a “sensitive species” filter set by regional reviewers that hides specific sites.

You might also be thinking: “I’m not a bird expert, what if I make mistakes?” – don’t worry! eBird data is constantly curated by regional reviewers that will ensure that the information is as accurate as possible. When potential mistakes are noticed, you will be notified via email. Moreover, when you are submitting data via the eBird application, the platform will flag out potential rarities that will allow you to enter specifics of your sightings. These filters are constantly reviewed and updated by the local expert (the eBird reviewer) to ensures that the flags do not appear irrelevantly. Uploading photographs and sound recordings will also be helpful, as not only is the reviewer able to check the data, any eBird user is able to report incorrect identifications. Similarly, you might be apprehensive about the perceived “quality” of the data you are contributing: “what if all the birds are common and boring? Won’t such data be useless?” – the answer is no! Data of all species – however common they are – are very valuable when conducting scientific research and consequently conservation planning. For example, if there is a site with 100 checklists per month, mostly filled with common species such as Yellow-vented Bulbuls P. goiavier and Brown-throated Sunbirds Anthreptes malacensis, we can be quite sure that conclusions we make based on information from the area is fairly accurate. Conversely, if checklists at such sites are not created because the species assemblage is “mundane”, the area will end up becoming a big question mark – could there be an undetected population of Greater Green Leafbirds Chloropsis sonnerati hiding there? Could there be huge numbers of introduced waxbills colonising the place? Furthermore, species that we think as “common” today might not continue to be in the future and vice versa. For example, the Red-wattled Lapwing Vanellus indicus, ubiquitous in most grassfields in Singapore today, was actually a locally rare bird just 20 years ago (Lok & Subaraj, 2009; Wang & Hails, 2007)! A steady stream of checklist will tremendously improve the data quality.

In Singapore, many of us share our sightings through social media sites such as Facebook groups or Telegram/WhatsApp groups; the eBird patronship fraction in our community is still relatively low. However, the number of eBirders has been rapidly picking up since ~2015, and the impacts of this increased usership have been tremendous. For example, Singapore’s first Siberian House Martin Delichon lagopodum and Hair-crested Drongo Dicrurus hottentottus were only discovered months after the birds were gone by A/P Frank Rheindt from the NUS Avian lab when he was scrolling through eBird photographs of the similar looking Asian House Martin Delichon dasypus and Crow-billed Drongo Dicrurus annectans. Similarly, counts from eBird were very useful in quantifying the sheer oddity of the 2019/2020 migration season we enjoyed two years back, especially for species including the Red-rumped Swallow Cecropis daurica and Whiskered Tern Chlidonias hybrida (Sin, Ng, & Kennewell, 2020). Data are not just restricted to members from the Cornell lab, but can be downloaded by any citizen-scientist or researcher upon request. These database, unlike information that are stored in notebooks, scattered pdfs, or people’s memory, are easily searchable and accessible. Both scientific and conservation action can be achieved with fine scale information, to which you can be a part of.

eBird data confirmed that the Red-rumped Swallow occurred in very high numbers during the 2019/2020 migratory season. This photograph was taken in Japan. Photo credit: Keita Sin

With all that said, I hope this article has broadened your perspective on how you can be an important contributor to bird science as well as improve the birding experience in our local scene!

Acknowledgements

A massive, massive thanks to Martin Kennewell (Singapore’s eBird reviewer) for the constant efforts in promoting the platform locally as well as taking on the tremendous task of moderating the data throughout the past few years. I also thank my team members from the Singapore Bird Project (Dillen, Francis, Movin, Raghav, Sandra), as well as Tan Hui Zhen and Geraldine Lee for comments on this article. Last but not least, a huge thanks to all eBird users out there, and if you are not one, I hope this article has convinced you to be one!

Disclaimer: Cornell is not paying me to write this article and I am also not presently involved in any research with them at the moment (I wish they did, and I wish I were!). I am an ardent eBird user and believe in the importance of data sharing and accurate data curation by the appropriate reviewer.

Literature cited

Sin, Y. C. K., Ng, D., & Kennewell, M. (2020). An unprecedented influx of vagrants into Malaysia and Singapore during the 2019–2020 winter period. BirdingASIA, 33, 142-147. Link: https://avianevonusdotcom.files.wordpress.com/2020/09/sin-et-al-2020_unprecedented-influx-of-vagrants-into-malaysia-and-singapore-2019-2020-1.pdf

Sullivan, B. L., Wood, C. L., Iliff, M. J., Bonney, R. E., Fink, D., & Kelling, S. (2009). eBird: A citizen-based bird observation network in the biological sciences. Biological Conservation, 142(10), 2282-2292. Link: https://www.researchgate.net/profile/Rick-Bonney/publication/248200195_eBird_A_citizen-based_bird_observation_network_in_the_biological_sciences/links/5747432808ae14040e28cf96/eBird-A-citizen-based-bird-observation-network-in-the-biological-sciences.pdf

Lok, A., & Subaraj, R. (2009). Lapwings (Charadriidae: Vanellinae) of Singapore. Nature in Singapore, 2, 125-134. Link: https://lkcnhm.nus.edu.sg/wp-content/uploads/sites/10/app/uploads/2017/06/2009nis125-134.pdf

Wang, L. K., & Hails, C. J. (2007). An annotated checklist of the birds of Singapore. Raffles Bulletin of Zoology Supplement, 15, 1-179. Link: https://lkcnhm.nus.edu.sg/publications/raffles-bulletin-of-zoology/supplements/supplement-no-15/

Extinction – what it means for birds in Singapore

Extinction is an evocative word, with some of the world’s most iconic birds such as the Dodo Raphus cucullatus and the Passenger Pigeon Ectopistes migratorius having achieved infamy for the dubious distinction of belonging to this category. Though the term often implies a sense of permanent loss, there are scenarios where extinction is not forever.

There are a few ways to think of the term ‘Extinct’.

The most commonly understood definition of extinction describes a complete global disappearance of a species. In Southeast Asia, no bird has been officially regarded as Extinct by the International Union for the Conservation of Nature (IUCN), though some species such as the Javan Lapwing Vanellus macropterus almost certainly are. The IUCN requires the criteria—exhaustive surveys in known and/or expected habitat, at appropriate times (diurnal, seasonal, annual), throughout its historic range have failed to record an individual—to be satisfied before concluded that a species is Extinct. This is to prevent a loss of directed conservation attention for a species that may actually be very rare rather than gone forever.

A prime example of this would be the recent extinction declaration of the Ivory-billed Woodpecker Campephilus principalis, only made after 77 years after the last confirmed sighting of this conspicuous bird. Such long lag times between last sightings of a species and a formal extinction declaration is not uncommon, especially is species that have historically had large geographic distributions.

Another category is species that are Extinct in the Wild, with all known populations of the species known only from captivity. No birds from the region officially fall into this category, though the newly split Javan Pied Starling Gracupica jalla and Javan Green Magpie Cissa thalassina may qualify with further research.

In both cases, the declaration of extinction is fairly clear-cut. If the bird can no longer be found in the wild, then it will naturally qualify for one of the two categories. However, it is when we begin to incorporate national boundaries into definitions of extinction where things begin to get hazy.

Local extinction describes a scenario where a species is extinct, or no longer occurs, within a specific portion of its geographic range. In many cases, a species may entirely vanish from a country—a situation which we describe as extirpation. Many bird species are extirpated from Singapore. For instance, both the Great Slaty Woodpecker Mulleripicus pulverulentus and Moustached Babbler Malacopteron magnirostre have not had breeding populations in the country for decades (Wang & Hails, 2007). In these cases, extirpation describes a situation where a bird is no longer a Resident Breeder; even though occasional individuals may stray into our shores from elsewhere. The lack of a breeding population precludes them from being considered re-established.

Moustached Babbler in Taman Negara, Pahang. Photo Credit: Keita Sin
Moustached Babbler in Taman Negara, Pahang. Photo Credit: Keita Sin

Record Committees (RCs) are often the local authority for declaring a bird nationally extinct. However, since national boundaries do not present actual barriers to the movement of birds, this task is much more complex than it first appears. Birds that show up unexpectedly could represent a hidden, breeding population of a very rare species or merely visitors from across the border—how does one make a case either way?

Great Slaty Woodpecker in flight, Taman Negara, Pahang. Photo Credit: Keita Sin
Great Slaty Woodpecker in flight, Taman Negara, Pahang. Photo Credit: Keita Sin

In complex cases such as this, members of the RC will have to evaluate records on a case-by-case basis, taking into account the movement and breeding ecology of the species. Many RCs additionally comprise multiple people, so as to utilise a broad swathe of expertise instead of relying entirely on the knowledge of single individuals, whose judgment may be clouded by various biases.

Let us use the previously mentioned Great Slaty Woodpecker and Moustached Babbler as examples.

Great Slaty Woodpecker perches on the side of the tree in Bukit Timah Nature Reserve. Photo Credit: Dillen Ng
Great Slaty Woodpecker perches on the side of the tree in Bukit Timah Nature Reserve. Photo Credit: Dillen Ng

In 2018, a single, Great Slaty Woodpecker was sighted within Singapore’s central forests, staying for only a short while before disappearing. Though the identification of the bird is without doubt, Great Slaty Woodpeckers are conspicuous and noisy birds (Eaton et al., 2021) — it is unlikely that an undetected population has persisted unnoticed on a small island. In addition, large woodpeckers are known to move large distances when searching for suitable foraging locations (Ogasawara et al. 1994; Garmendia et al., 2006). A single bird flying the comparatively short distance from Johor to Singapore would be unremarkable when these woodpeckers are known to fly much greater distances. As such, taking the collective evidence into account makes us suspect that the Great Slaty Woodpecker presents a case where the bird is merely a visiting individual and not part of a larger, undetected population on the island.

Moustached Babbler at Panti Forest. Photo Credit: Francis Yap

However, the ecology of the Moustached Babbler and other understory babbler species such as the Fluffy-backed Tit-babbler Macronus ptilosus is far different. Anyone who has searched for babblers can attest to their penchant for hiding in thick cover and their reluctance to move into the open. This trait suggests that most babblers do not often move across large landscapes without forest cover (Yong, 2006). In addition, the relatively short, rounded wings of most understory babblers indicate that they are poor fliers and unlikely to undertake long-distance movements (Desrochers, 2010; Hermes et al., 2016). As such, if a population of a presently unrecorded babbler species were suddenly re-discovered in Singapore, we would not suspect that these birds were visitors from abroad. However, if these birds were encountered in a site that was regularly birded, we might suspect that these birds were recent releases/escapees. Babblers are highly vocal birds with distinctive calls and would surely have been recognised by local birders had they been present as a breeding population (Eaton et al., 2021).

The Fluffy-backed Tit-babbler is an understory species that is not known to undertake long-distance movements. This individual is from Lenggor, Johor. Photo Credit: Keita Sin

As you can see, nothing is ever quite so clear cut!

These examples offer some insight into the thought processes that we might undertake when confronted by new records. Though it is a rather complex and multifaceted process, we hope that this article makes what seems like a rather opaque and fuzzy process much more understandable!

References

Desrochers, A. (2010). Morphological response of songbirds to 100 years of landscape change in North America. Ecology 91: 1577–1582. doi: 10.1890/09-2202.1

Eaton, J. A., van Balen, S., Brickle, N. W., & Rheindt, F. E. (2021). Birds of the Indonesian Archipelago: Greater Sundas and Wallacea (Second Edition). Lynx Edicions, Barcelona.

Garmendia, A., Cárcamo, S., & Schwendtner, O. (2006). Forest management considerations for conservation of black woodpecker Dryocopus martius and white-backed woodpecker Dendrocopos leucotos populations in Quinto Real (Spanish Western Pyrenees). In Forest Diversity and Management (pp. 339-355). Springer, Dordrecht. Link

Hermes, C., Döpper, A., Schaefer, H. M., & Segelbacher, G. (2016). Effects of forest fragmentation on the morphological and genetic structure of a dispersal-limited, endangered bird species. Nature Conservation16, 39. Link

Ogasawara, K., Izumi, Y., & Fujii, T. (1994). The status of black woodpecker in Northern Tohoku District, Japan. Journal of the Yamashina Institute for Ornithology, 26(2), 87–98. Link

Extinction – what it means for birds in Singapore

Yong, D. L., (2006). Preliminary list of larger vertebrates in Panti Forest Reserve, South Johore. Singapore Avifauna, 20(1): 26–35. Link

 

 

 

 

 

 

Bird List Revision for September 2021 – Special Edition

The Singapore Birds Project checklist is updated regularly according to taxonomic updates by the International Ornithological Committee (IOC). Our team recently conducted a thorough review to vote on additional species to be added to or removed from the checklist. In the spirit of ensuring that accurate information is provided in a timely fashion, we decided to release a Special Edition prior to the next IOC update. The downloadable list (in Excel format) is available HERE.

Along with this update, we would like to welcome Raghav to the team. Our growing Singapore Birds Project main team consists of Keita Sin (chair), Sandra Chia (vice-chair), Dillen Ng, Francis Yap (site admin), Movin Nyanasengeran and Raghav Narayanswamy. Many of you have provided us generous comments for our work which we are very grateful for. Suggestions and constructive criticisms, as always, are strongly welcome! Please feel free to reach out to us via the Contact Us section.

A write-up of how our checklist operates will be released soon. In the mean time, here are the details for the changes to the checklist.

Added

Orange-breasted Green Pigeon: A vagrant to Singapore with a single record of a male from Japanese Garden on 22 December 2007.

Masked Lapwing: This species native to Australia has breeding records dating back to at least 2004. The growing population seems to be sustainable and recent sightings include a flock of ~50 birds along a canal in Bedok.

Javan Plover: A single, very likely breeding record from Pulau Tekong in mid-2021. More records of this expanding species might be expected in the near future.

Milky Stork and Painted Stork: Both species of storks have been introduced to Singapore since at least 1987. Their breeding is indicated by ever-present juveniles at multiple sites in Singapore coupled with the numerous nests around Mandai. A recent genomic analysis by Baveja et al (2019) revealed an alarming result that many of the storks in Singapore are hybrids at some level. However, some genetically pure Milky Stork still exists. The Painted Storks sampled in the study were at best backcrosses between first generation hybrids and pure ones, but this species is also added to the checklist on balance that evidence suggest the presence of pure individuals.

Pied Kingfisher: A single record from Punggol on 18 September 1995. The same species was recorded at Southern Johor in early 2016 as well.

Crimson-winged Woodpecker: Sightings from Bukit Timah in 2001, at least one of which was accompanied by sketches. Several other reports continuing up to 2008 are unsubstantiated thus far.

Monk Parakeet: This species is native to South America and has been present since at least 2009, with nesting records dating back to 2012. The presence of multiple breeding records coupled with the recent westward expansion is indicative of an alarming population growth.

Velvet-fronted Nuthatch: Multiple sightings of a single individual in Bukit Timah from 1996 to 1999. A non-breeding visitor to Singapore.

Red-billed Starling: A total of four records in Singapore. While the provenance of each specific record remains to be assessed, increasing evidence of vagrancy from Indochina and the Philippines are indicative that wild birds occur in Singapore.

Golden-backed Weaver: The proliferation of this species in suitable habitats has been highly visible. Strongholds at Kranji Marshes and Lorong Halus show that this species is clearly well-established. The obvious displacement of native Baya Weavers is worrying.

Deleted

Yellow-crested Cockatoo: This introduced species only occurs in small numbers in Singapore, indicative that there is a lack of a self-sustaining population. Multiple reports of hybridising Yellow/Sulphur x Tanimbar Cockatoos are also strongly suggestive that individuals are struggling to find mates from their own species. Moreover, Sulphur-crested Cockatoos are more numerous than this species.

The following species were deleted from our checklist on the basis that there have not been any conclusive records in the nation for over 30 years.

Eurasian Teal, Dunlin, Roseate Tern, Hen Harrier, Plain Sunbird, Yellow-breasted Bunting, Eurasian Woodcock, Blyth’s Hawk-Eagle, Oriental Hobby

Shifted to Annex

This category houses species that have been recorded in the vicinity of Singaporean waters in the past 30 years. One should keep a lookout as there is a chance that these birds can be encountered within our national boundaries during pelagic trips. We keep an open mind about pelagic species and consider both quantitative (GPS coordinates) and qualitative evidences (descriptions of the sighting and ecological background of the species) when assessing such birds.

Lesser Black-backed Gull: A record from 20 November 2011 along the Singapore Straits with an unfortunate lack of GPS coordinates nor detailed descriptions.

Christmas Frigatebird: A single record outside Singapore waters from 4 May 2013.

References

Baveja, P., Tang, Q., Lee, J. G., & Rheindt, F. E. (2019). Impact of genomic leakage on the conservation of the endangered Milky Stork. Biological Conservation, 229, 59-66.

An Indonesian Archipelago Wishlist: Birds to Look Out For

The recent sighting of the Javan Plover Charadrius javanicus at a reclaimed site northeast of Singapore island was exciting yet unsurprising. Exciting because it was a first for Singapore and continental Southeast Asia that caught everyone off guard (then again, none of us are really prepared for megas!) and unsurprising because this is a species whose range has been slowly expanding over the years (Iqbal et al., 2011; Eaton et al., 2021). The appearance, and likely breeding of this species is highly relevant to recent changes in regional avifauna, especially when taking into account the first breeding records for the Pied Stilt Himantopus leucocephalus and Black-winged Stilt H. himantopus that were documented at the same site in 2019 and again this year, respectively.

Apart from the Javan Plover, several other species traditionally known to be from the Indonesian Archipelago (that comprises Sumatra, Borneo, Java and other Indonesian islands west of the Wallace Line) could potentially be found in Singapore and the neighbouring regions. Here are the distinguishing features of the Javan Plover and seven other species readers can keep an eye out for!

Javan Plover Charadrius javanicus

This species closely resembles the Kentish Plover, a locally uncommon migrant. Features including warm buff ear-coverts and relatively heavier bill and longer legs point to the Javan Plover. For those keen to learn more, detailed distinguishing features are described in Iqbal et al. (2013). Other regular plovers in Singapore can be distinguished by a combination of several other features. Lesser and Greater Sand Plovers have incomplete white-bands on their neck, Malaysian Plover have more “sandy-looking” upperparts, and White-faced Plover has a plain looking face as its name suggests.

Wandering Whistling Duck Dendrocygna arcuata

Although this species used to be an uncommon introduced species (Wang & Hails, 2007), the last local sighting was in 2016 (eBird) and the feral population has likely crashed for good. Being highly dispersive, wild birds could possibly wander here in due time. In fact, there is a record from Perak, Malaysia, that may conceivably be of wild provenance (but note that the current status of this species in Peninsula Malaysia is also introduced). It can be distinguished from the locally uncommon Lesser Whistling Duck by its lack of yellow eye ring and distinct white flanks.

Sunda Teal Anas gibberifrons

A species that seems to be undergoing a rapid range expansion across Borneo, Sulawesi and Sumatra (Eaton et al., 2016; 2021; Iqbal, 2016; MNSBCC Records Committee, 2016). With records in Sumatra not too far from Singapore, this funny looking duck might make its way here in the near future. It is much darker and browner than the local Whistling Ducks, with a distinct bulge on the male’s forehead. It prefers brackish water although other wetland habitats are also possible sites to look out for this species. Although various breeds of domestic ducks have been released in Singapore, these typically look more Mallard-like, with variable amount of colouration on their heads and wingpanels. Having said that, most if not all wild ducks in Singapore are typically worth celebration, so if in doubt of identification, it’s best to share the sighting for confirmation.

Black-backed Swamphen Porphyrio indicus

Swamphen taxonomy is rather incongruent, with much left to be discovered (Garcia-R & Trewick, 2015; Callaghan et al., 2020; Eaton et al., 2021; Gill et al., 2021). Records from Singapore are thought to be the Grey-headed Swamphen viridis (Wang & Hails, 2007; Callaghan et al., 2020), but possible integrades have been recorded before locally (Wells, 1990). The distribution of the Black-backed Swamphen is also contentious especially on Sumatra, with the two forms likely mixing (Wells, 1999; Taylor, 2020; Eaton et al., 2021). The Grey-headed Swamphen is another species struggling to survive in Singapore – a common theme for local waterbirds – and was last seen in 2018 (eBird). But if you do happen to see one, be sure to check its back colour. Black-backed Swamphen can be distinguished by having darker upperparts and face.

Australasian Grebe Tachybaptus novaehollandiae

The Australasian Grebe is capable of undertaking overwater dispersals (Llimona et al., 2020). Recent new records from Sulawesi and southern Sumatra (Eaton et al., 2016; Eaton et al., 2021) suggest a possible range expansion underway. Its habitat requirements are similar to the locally rare Little Grebe Tachybaptus ruficollis from which it can be distinguished by its darker neck and ear coverts. Given that the Little Grebe is already struggling to survive in Singapore at the moment, the chances of the Australasian Grebe breeding here like the plovers did are probably low, but they’re certainly worth looking out for.

Little Black Cormorant Phalacrocorax sulcirostris

Another species that seems to be experiencing a spread across the Sumatran coast (Eaton et al., 2021). Waterbodies – both coastal and inland – are potential locations to find this species. Locally, escaped individuals of the Great Cormorant and Little Cormorant have been documented (Wang & Hails, 2007). There were apparently two local records of the Little Black Cormorant as well in August and September 1993 (Oriental Bird Club, 1994; Lim, 2009). Assessing the provenance of cormorants can be a challenge in Singapore so do try to obtain high quality images of them (especially the legs) if you find one.

Little Egret Egretta garzetta nigripes

Knowledge on the distribution of this taxon in our region is far from ideal. Present from Indonesia through eastern Australia, it seems to be spreading across Sumatra (Iqbal, 2012; del Hoyo et al., 2020; Eaton et al., 2021). Their local status varies from “uncommon”, “sparing” to “probable” (Wang & Hails, 2007; Robson, 2014; Puan et al., 2020) and there is still much for us to document. Possible integrades have been seen in Singapore too. Various bare part colouration distinguishes this taxon apart from the locally common migrant Little Egret garzetta (Bakewell, 2019), perhaps most distinct among them being their toe colour – black in nigripes, yellow in garzetta in breeding plumage (images 14 & 15). However, caution should be taken during identification as juveniles and non-breeding garzetta can have duller feet and mud can affect feet colour (Robson, 2014).

 

Sacred Kingfisher Todiramphus sanctus

This species breeds in Australia and is a highly likely contender for showing up on Singapore given that it is an Austral migrant to Borneo and Indonesia, similar to the Horsfield’s Bronze-cuckoo Chrysococcyx basalis. Multiple people have claimed an encounter with this species in Singapore and it is also listed to be present in Robson (2014). However, none of the records have been adequately substantiated and a record from Thailand in February 2019 (Round et al., 2020) is the only formal record in our region thus far. The Sacred Kingfisher can be distinguished from the Collared Kingfisher T. chloris by its turquoise upperparts (as opposed to blue), smaller overall size and bill, and buff wash on its lores and flanks. Care is required in distinguishing this species from immature Collared Kingfishers as they can show some buff wash as well, but typically with scalloped plumage on their breast.

Acknowledgements

Huge thanks to Dave Bakewell, James Eaton and Khaleb Yordan for identification discussions on the Javan Plover identification online, as well as others we had offline. I would also like to express my gratitude to Frankie Cheong for documenting and sharing pictures of Singapore’s first Javan Plover, to the Singapore Birds Project team (Dillen, Francis, Movin, Raghav, Sandra) for comments on this article and to the following for sharing their excellent photos: Dillen Ng, Geraldine Lee, Goh Cheng Teng, Khaleb Yordan and Lim Hong Yao.

Literature Cited

Bakewell, D. (2019). The Chinese Egret Egretta eulophotes: identification revisited. BirdingAsia, 31, 14-23.

Callaghan, C. T., Pranty, B., Pyle, P., & Patten, M. A. (2020). Gray-headed Swamphen (Porphyrio poliocephalus), version 1.0. In Rodewald, P. G. & Billerman, S. M. (Eds.), Birds of the World. Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bow.purswa3.01

del Hoyo, J., Martínez-Vilalta, A., Motis, A., Collar, N., Kirwan, G. M., & Christie, D. A. (2020). Little Egret (Egretta garzetta), version 1.0. In Billerman, S.M., Keeney, B.K., Rodewald, P.G. & Schulenberg, T.S. (Eds.), Birds of the World. Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bow.litegr.01

Eaton, J. A., van Balen, S., Brickle, N. W., & Rheindt, F. E. (2016). Birds of the Indonesian Archipelago: Greater Sundas and Wallacea. Lynx Edicions, Barcelona.

Eaton, J. A., van Balen, S., Brickle, N. W., & Rheindt, F. E. (2021). Birds of the Indonesian Archipelago: Greater Sundas and Wallacea (Second Edition). Lynx Edicions, Barcelona.

Garcia-R, J. C., & Trewick, S. A. (2015). Dispersal and speciation in purple swamphens (Rallidae: Porphyrio). The Auk: Ornithological Advances132(1), 140-155. Link: https://academic.oup.com/auk/article/132/1/140/5149144?login=true

Gill, F., Donsker, D. & Rasmussen, P. (Eds). (2021). IOC World Bird List (v11.2). doi:10.14344/IOC.ML.11.2

Iqbal, M., Febrianto, I., & Zulkifli, H. (2011). The occurrence of the Javan Plover Charadrius javanicus in Sumatra, Indonesia. Wader Study Group Bulletin, 118(2), 131-133.
Link: https://www.researchgate.net/publication/293205017_The_occurrence_of_the_Javan_Plover_Charadrius_javanicus_in_Sumatra_Indonesia

Iqbal, M., Nurza, A. & Giyanto. (2012). Breeding Records of Little Egret Egretta garzetta in Sumatra, with notes on the occurence of race E. g. garzettaKukila16, 59-63.
Link: https://www.researchgate.net/publication/315912527_Breeding_Records_of_Little_Egret_Egretta_garzetta_in_Sumatra_with_notes_on_the_occurence_of_race_E_g_garzetta

Iqbal, M., Taufiqurrahman, I., Gilfedder, M., & Baskoro, K. (2013). Field Identification of Javan Plover Charadrius javanicusWader Study Group Bulletin120(2), 96-101.
Link: https://www.researchgate.net/publication/262562330_Field_identification_of_Javan_Plover_Charadrius_javanicus

Iqbal, M. (2016). Status of Sunda Teal Anas gibberifrons in South Sumatra. Kukila19, 30-33.
Link: https://www.researchgate.net/publication/316075498_Status_of_Sunda_Teal_Anas_gibberifrons_in_South_Sumatra

Lim, K.S. (2009). The Avifauna of Singapore. Nature Society (Singapore), Singapore.

Llimona, F., del Hoyo, J., Christie, D. A., Jutglar, F., Garcia, E. F. J., & Kirwan, G. M. (2020). Australasian Grebe (Tachybaptus novaehollandiae), version 1.0. In del Hoyo, J., Elliott, A., Sargatal, J., Christie, D.A. & de Juana, E. (Eds.), Birds of the World. Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bow.ausgre1.01

MNSBCC Records Committee. (2016). Latest News 22 November 2016. MNSBCC Records Committee. Retrieved 28 August 2021 from https://sites.google.com/site/mnsbccrecordscommittee/Home/latest-news

Oriental Bird Club. (1994). From the field. Oriental Bird Club Bulletin, 19, 65-67.
Link: https://www.biodiversitylibrary.org/item/253243#page/69/mode/1up

Puan, C.L., Davison, G. & Lim, K.C. (2020). Birds of Malaysia. Lynx Edicions, Barcelona.

Robson, C. (2014). Field guide to the birds of South-East Asia (Second Edition). Bloomsbury Publishing, London.

Round, P D., Jahan, I., Thompson, P. & James, D. J. (2020). Mainland Asia’s first record of Sacred Kingfisher Todiramphus sanctus. BirdingAsia, 34, 123-127.

Taylor, B. (2020). Black-backed Swamphen (Porphyrio indicus), version 1.0. In Rodewald, P.G. (Eds.), Birds of the World. Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bow.purswa4.01

Wang, L. K., & Hails, C. J. (2007). An annotated checklist of the birds of Singapore. Raffles Bulletin of Zoology15, 1-179.
Link: https://lkcnhm.nus.edu.sg/wp-content/uploads/sites/10/app/uploads/2017/04/s15rbz001-179.pdf

Wells, D.R. (1990). Malayan Bird Report: 1986 and 1987. Malayan Nature Journal, 43, 172-210.

Wells, D. R. (1999). The birds of the Thai-Malay peninsula (Vol. 1). Academic Press, London.