Asian Openbill

posted in: Morphology-Develop. | 0

“Asian Openbills (Anastomus oscitans) are common birds in Peninsular Malaysia after their mass movement south some years back. Any visit to the Perak wetland areas will witness 200-400 birds. I had, in the past, erroneously assumed that birds that are darker (greyer) were immature. However, on this visit more than 70% looked ‘greyer’.

“I looked at Hancock et al (2010) for some guidance and they state:

“’Adult plumage is predominantly white, with black in the wings and tail. The bill is a dull greenish-horny colour, mottled and streaked with black and reddish …. Before the onset of breeding, probably through a moult, the greyish plumage becomes immaculate white and the black feathers take on an iridescent purplish green. The white changes back to grey soon after the eggs are laid, in a process not well understood, presumably through feather wear and/or soiling.’… ‘Immature birds are a darker grey than adults and the head and neck are browner; they have a blackish brown mantle, wings and tail. The legs and feet are pale horn colour (often streaked with white droppings). The short bill is dark and has little or no gap until the bird is approximately 4-6 months old.’

“Kazmierczak (2000) states ‘juvenile much greyer and initially without the bill opening’. Grimmett et al (2011) state ‘largely white (breeding) or greyish-white (non-breeding) ….. juvenile has brownish-grey head, neck and breast, and brownish mantle ….’

“The four different birds I am posting here all have less than ‘pure’ white plumage and are speckled grey. They all have an open bill, suggesting that they are not juveniles.

“However, the ones shown above and below have some brown in the neck. The bird above has a wing moult in progress.

“A close look at the bill in the above two birds shows them to be lighter and flacking off (?moult – if we can use this for bills). Wonder if these two can then be called immature? A higher resolution close up of the bill in bird above (see below) shows the bill ‘moult’ (for lack of a better word).”

Dato’ Dr Amar-Singh HSS
Ipoh, Perak, Malaysia
3rd December 2019

Location: Perak, Malaysia
Habitat: Wetlands, Padi Fields

Reference:
1.
James Hancock, James A. Kushlan, M. Philip Kahl, Alan Harris, David Quinn. Storks, Ibises and Spoonbills of the World. Helm Identification Guides. 2010.
2. Krys Kazmierczak. A Field Guide to the Birds of the Indian Subcontinent 2000 (paperback copy printed 2008).
3. Richard Grimmett, Tim Inskipp, Carol Inskipp. Birds of the Indian Subcontinent. 2nd edition 2011.

5+

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.