First occurrence of an Ashy-headed Green Pigeon in Singapore

This post examines the first recorded occurrence of a male Ashy-headed Green Pigeon at Singapore's Central Catchment Nature Reserve. It outlines the diagnostic features that distinguish the species from other local green pigeons and discusses the debate surrounding its status as either a wild vagrant or an escapee.

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 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 Pink-necked Green Pigeon T. vernans Male has pink neck, green wings Male Pink-necked Green Pigeon at Jelutong Tower 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 Cinnamon-headed Green Pigeon T. fulvicollis Male has orange head Male Cinnamon-headed Green Pigeon at Tampines Eco Green Little Green Pigeon T. olax Male has grey head and white iris Male Little Green Pigeon at Jelutong Tower 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 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 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 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...