Juvenile White-bellied Sea-eagle – moulting

posted in: Feathers-maintenance, Raptors | 0

A pair of White-bellied Sea-eagles (Haliaeetus leucogaster) nesting in a tree at Fort Canning Park had seen their chick fledged. It was testing its flying ability as seen below with its wings outstretched exposing the underside of its flight feathers. At the same time the series of tail feathers are fanned out.

Feathers are not permanent structures. They are shed periodically and then replaced. This is known as moulting. Moulting helps replace damaged and worn-out feathers. And when feathers happen to be torn off as when attacked by another bird or a predator, they are also replaced by new feathers.

James Gan’s image of the juvenile White-bellied Sea-eagle pulling out a feather was documented in Fort Canning. Any fledged feather will drop off automatically. In this instance the feather must have remained on the body after moulting and the sea-eagle must have been uncomfortable with it still lodged among the other feathers. Thus it grasped the shaft to pull the feather away.

According to Ginn & Melville (2007), the juvenile of certain species of birds undergo a complete moult of all the plumage soon after fledging. Whether the White-belllied Sea-eagle is among them is not known. Anyway, moulting of tropical birds, especially raptors is not well studied in this part of the world.

If there is any ornithologist well versed with moulting among raptors, your input will be most welcome.

James Gan
Singapore
24th June 2018

Reference:
Ginn, H.B. & D.S. Melville (2007). Moult in birds. British Trust for Ornithology, Guide No. 19, The Nunnery, Thetford, Norfolk. 112pp.

This post is a cooperative effort between Birds, Insects N Creatures Of Asia and BESG to bring the study of birds and their behaviour through photography and videography to a wider audience.

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