Author: raghavnarayanswamy

Another week, another rare bird at Chek Jawa! The Stripe-throated Bulbul Pycnonotus finlaysoni is another bird previously recorded in Singapore, just in April last year in fact. The details were first published online two months ago and last month the Records Committee came to the conclusion that this bird, recorded at Upper Seletar Reservoir, was more likely an escapee than a wild bird. With the recent sighting at Chek Jawa, some key discussion points have changed, so we reconsidered the previous record again alongside our review of the Chek Jawa bird. 

After extensive deliberation our committee reached split decisions on both records, and with no majority of votes in favor of treating either bird as being wild, the species has been placed in Category D. Category D species are not in the Singapore Bird Checklist; they would otherwise appear in Category A, but there is reasonable doubt that the records are of truly wild birds. (The exact vote counts for the Chek Jawa bird were 4 wild, 4 escapee; and for the Upper Seletar bird, 3 wild, 5 escapee.)

There are a considerable number of points to consider in favor of both sides, and we will summarize them below. Ultimately, there are no clear answers, but we aim to use the evidence available to weigh the likelihoods of each scenario. The fact that several committee members did not vote in the same way is a feature of our robust process, and signifies the difficulty in assessing these records. The end result or categorization of a species is also by no means set in stone; rather it is open to change as and when new information becomes available. 

Feather condition

There are no indications that the feather condition is poor or unnatural. However, bulbuls are small birds, kept extensively in captivity – it is not hard to find a bulbul in a pet shop with normal feathers. 

Status in the pet trade

The Stripe-throated Bulbul is a songbird kept extensively in captivity across Southeast Asia (Chng & Eaton, 2016; Limparungpatthanakij, 2022). It is often kept for cross-breeding with Red-whiskered Bulbuls, and records from Bangkok, which is in the middle of the species’s range, are treated as escapees due to their high prevalence in the pet trade. The increasing scarcity of Red-whiskered Bulbuls in the wild due to trapping is also likely contributing to higher trapping pressure on other bulbuls with pleasant songs, including Stripe-throated – leading to more possible sources of escapee Stripe-throated Bulbuls across the region (Limparungpatthanakij, 2022). YouTube searches for this species’s Thai and Malay names reveal hundreds of hits, several ostensibly advertising their video as a means to trap wild Stripe-throated Bulbuls. Several others feature birds in cages, many of which appear to have normal feather condition. While we did mention previously that you can “find and buy nearly anything in a cage these days”, the volume of trade in this species is likely to be extremely high in comparison to the birds we’ve been getting so far (SBP, 2023). What’s important here is that more than simply being ‘present’ in the regional pet trade – which by itself does not really indicate anything – it is quite a popular species as well. Its high presence in captivity elsewhere in the region may indicate popularity locally as well; the regional pet trade is closely intertwined. Anonymous sources have also informed us that this species is locally traded.

Habitat/Location

Chek Jawa is a prime location for visitors to turn up, and the location is an argument against the escapee hypothesis. But we do have surprisingly many records of introduced bulbuls on Pulau Ubin, including Black-crested and Red-whiskered. Either these birds are adept at dispersing from our main island, or they have been kept on Ubin at some point, or there is some kind of hidden influx of wild Black-crested and Red-whiskered Bulbuls from further north. The last possibility is near impossible to verify and best treated as unlikely given these species are also highly traded in captivity, and the first two would unfortunately throw this bird’s origins into question too. 

Having said that, the location is still a point in favor of the case that the bird is wild.

Status in southern Peninsular Malaysia

eBird range map for Stripe-throated Bulbul. Here is a link to the map if it does not load immediately. This simplified map does not do a good job of illustrating how rare this species in Johor (zoom in to view the the full eBird map with hotspot pins for a clearer impression). 

Many of the species which have recently been added to our checklist, or recorded as visitors (see Table 1 below) are indeed quite scarce in Johor. Examples include the Scarlet-breasted Flowerpecker, Black-and-white Bulbul, and White-crowned Hornbill. However, the Stripe-throated Bulbul is markedly rarer than all of them in Johor, even though it is known to tolerate more degraded habitats than those species. All time eBird records for Panti show well over 100 records of Black-and-white Bulbul and Scarlet-breasted Flowerpecker and at least 10 of White-crowned Hornbill, yet only 5 of Stripe-throated Bulbul. Similar results have been observed from Gunung Bekok and Gunung Belumut in Johor. Surveys there found this species to be the second-least frequently encountered bulbul among the 15 species recorded, second only to Scaly-breasted Bulbul which has no confirmed records in Singapore (Peh et al., 2005).

Meanwhile, the Stripe-throated Bulbul is actually quite common in all sorts of habitat from Malacca northwards, so the very abrupt drop in abundance in the south suggests its dispersal outside its core range is infrequent.  This is also in contrast to the other species listed above, which are scarce to rare throughout their range. It would be more straightforward to construct a case for the species’s dispersal if it was more common, or becoming more common, in Johor, where vast areas of suitable habitat are available. At the same time, the deforestation explanation, which we believe is pushing several of these species out of Johor’s forests, does not apply as well here; the species is simply very tolerant of low-quality forest habitats, to the point that it appears to be benefiting from forest degradation across its range (Nor Hashim, 2013; Wells, 2007).

We did note, however, a recent sighting from Gunung Pulai Recreational Forest in Johor, which may indicate the early signs of a southward influx of this species. The good news is that we will probably have good indications that such an influx is occurring, with more observers at birding sites in Johor such as Panti and Lenggor. Our RC decisions are never cast in stone and constantly move with evolving evidence; please post your records on eBird or let us know if you see this species in Johor!

(a) Wang & Hails, 2007; (b) Wells, 1999; (c) Wells, 2007; (d) eBird

* Species with status “Limbo” are provisionally not accepted as wild birds in Category A but are placed in Category D, recognizing the possibility that the bird originated from captivity.

Table 1 Records of Sundaic visitors treated as very rare in our checklist, as well as other possible Sundaic visitors not included in our checklist, Jan 2022–present.

(Cover photo: Stripe-throated Bulbul at Chek Jawa on 9 May 2023. Photo credit: Raymond Siew.)

References

Chng, S. C. L., and J. A. Eaton (2016). Snapshot of an on-going trade: an inventory of birds for sale in Chatuchak weekend market, Bangkok, Thailand. BirdingASIA 25, 24–29. Link

Limparungpatthanakij, W. L. (2022). Stripe-throated Bulbul (Pycnonotus finlaysoni), version 2.0. In Keeney, B. K. & Maleko, P. N. (Eds.), Birds of the World. Cornell Lab of Ornithology, Ithaca, NY, USA. 

Nor Hashim, N. E. (2013). Comparative study of understorey birds inhabiting selected logged and virgin lowland forests. University of Malaya. Link

Peh, K. S.-H., Jong, J. de, Sodhi, N. S., Lim, S. L.-H., & Yap, C. A.-M. (2005). Lowland rainforest avifauna and human disturbance: persistence of primary forest birds in selectively logged forests and mixed-rural habitats of southern Peninsular Malaysia. Biological Conservation, 123(4), 489–505.

Singapore Birds Project. (2023). Singapore’s first wild White-crowned Hornbill. Link

Wang, L. K. & Hails, C. J. (2007). An Annotated Checklist of the Birds of Singapore. The Raffles Bulletin of Zoology, 15(Suppl), 1–179. Link

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

Wells, D. R. (2007). The Birds of the Thai-Malay Peninsula (Vol. 2). Christopher Helm, London.

In November 2022, word of a Black-headed Ibis at Sungei Buloh Wetland Reserve was spreading through birding circles like wildfire. Over six months later, we have another species previously recorded as an escapee, this time seen at Chek Jawa – the White-crowned Hornbill Berenicornis comatus. Kiri Zhang’s quick alert meant many were able to rush down and see the bird the same day, and despite some disappointing days when it wasn’t sighted, the bird seems to be still wandering around Chek Jawa today. 

Our Records Committee’s deliberations led us to the unanimous conclusion that this was likely a wild bird, although this was by no means a straightforward decision.

The identification was never in doubt. The entirely white tail and white crown rule out all other hornbill species in the region. The bigger question then – is it more likely to be a wild bird, a genuine visitor from Malaysia, or an escapee from someone’s collection? The RC’s discussions centred around a few issues which are summarized below.

Where does this species occur usually?

This is a typical Sundaic species, ranging from the forests of Kaeng Krachan in Phetchaburi, Thailand, to Johor. It also occurs in Sumatra and Borneo although we could not find any records from the Riau Archipelago in Indonesia. David Wells does not list this species from Johor in his 1999 book, although there are several recent observations at both Panti and Lenggor – the linked checklists are just a few of several on eBird.

eBird range map for White-crowned Hornbill. Here is a link to the map if it does not load immediately.

How regularly does this bird occur in the pet trade?

Hornbills appear in the wildlife trade mainly for their casques but are occasionally kept as pets as well. The White-crowned Hornbill is not well-represented in TRAFFIC surveys. It’s highly possible, though, that the species occurs infrequently in the regional pet trade. But its mere presence in the pet trade does not provide a strong case for why this particular bird must be escaped – one search of Shopee in Indonesia reveals that you can find and buy nearly anything in a cage these days. Our committee always aims to objectively weigh the relative likelihoods when dealing with these records, and while frequent occurrence in the pet trade is a red flag, there is no evidence that this species is recorded particularly often in captivity.

So, does the location matter?

Chek Jawa is currently seeing its second influx of Sundaic visitors in two years. Last year, we had a Large Woodshrike, Ruby-cheeked Sunbirds, Scarlet-breasted Flowerpecker, and best of all, two Black-and-white Bulbuls visiting the same trees frequented by the hornbill. The location is developing a reputation for attracting these wandering birds, and looking at a map it’s not hard to see why; it could be deforestation in Johor, just natural dispersal, or a combination of the two, driving them southwards in search of new habitats, and Chek Jawa would be one of the first places they land on.

The location also means that a bird which escaped from captivity on the main island would need to cover some distance and make a sea crossing in order to reach Chek Jawa in the first place. This strengthens the argument for this bird being a wild bird. 

What about the bird’s physical condition?

Nothing about the bird’s appearance suggests it has origins in captivity. The bird is not ringed, its bare parts show no signs of unnatural wear, and the feathers are in near-perfect condition; the tail feathers are perhaps very slightly tattered, but this is quite normal for any wild bird. Like all the other points, though, this in itself does not really prove anything, as a well-kept captive bird could theoretically be in good condition too. So this fact again merely lends a bit more credence to the argument that this bird was always wild.

What about all the other past hornbill records which have been treated as escapees?

This is really a very good question, and one we don’t know the answer to. Before this White-crowned Hornbill, Singapore has actually had several records of hornbills which have been classified as escapees.

The repeated Rhinoceros Hornbill sightings between 2004 and 2009 were accompanied by a Great Hornbill, and both birds spent several years in the Eng Neo area. Black Hornbills – at one point up to six birds, including immatures – were recorded between 1986 and 2003, mostly near the Upper Seletar/Nee Soon area. And of course, the White-crowned Hornbill was itself recorded previously, at the Singapore Botanic Gardens in 1987. 

In fact, several RC members have expressed doubts over the rather liberal application of the escapee tag for many historical records – and it’s not just restricted to hornbills. A few examples of past records the RC has previously re-evaluated and finally added into the checklist include the Velvet-fronted Nuthatch, Crimson-winged Woodpecker, Orange-breasted Green Pigeon, and even Pied Kingfisher. These were generally contemporaneously treated by past records-keepers as being escapees, although they share similarities with many of the birds we consider today to be genuinely wild dispersing birds. 

Last year, as a committee, we considered the Great Hornbill record from the Bukit Timah area in 2016 and 2017 and voted by a 6-2 margin to treat the record as an escapee instead of a wild bird. Part of that could be due to the species’s ecology and perhaps higher prevalence in the pet trade – see the record page for more information – but it also may be due to some degree of wariness to apply our Chek Jawa-tinted lenses of today to the past, where details of several records are rather sparse or provide few indications of why birds were considered escapees in the first place. If there were good reasons, we may indeed never know. And so while we have reviewed some past records, we felt those cases were more clear-cut inclusions in the checklist with especially strong claims for wild provenance. 

With this, the White-crowned Hornbill is now the 429th species on the Singapore Bird List. If you haven’t gotten your tick yet, maybe this is the motivation you need to go down and see this new visitor to our shores!

White-crowned Hornbill at Chek Jawa. Photo credit: Adrian Silas Tay

White-crowned Hornbill at Chek Jawa. Photo credit: Goh Cheng Teng

White-crowned Hornbill at Chek Jawa. Photo credit: Raghav Narayanswamy

White-crowned Hornbill at Chek Jawa. Photo credit: Jayden Kang

White-crowned Hornbill at Chek Jawa. Photo credit: Lim Qian Xun

References

Chan, Y. M., Chan, M., & Wee, Y. C. (2008). Aberrant behaviour of a female Great Hornbill and a female Rhinoceros Hornbill. Nature in Singapore, 1, 31–34. Link

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