Moulting 1

On and off I have been picking up various types of feathers in my garden and along my driveway (above: Javan Myna contour feather, top left; down, top right; tail, middle; Black-naped Oriole tail feather, bottom). During the time when I was interested in plants (and not in birds), I considered these as discarded feathers, detached as a result of fights between birds. Now that I am a “sometime-birdwatcher”, I am slightly more enlightened.

I now know that these feathers have been discarded naturally as a result of moulting. Now why do birds discard their feathers?

Feathers are important to birds. They insulate them from the cold and enable them to fly. But feathers undergo wear and tear. They become brittle, frayed and sometimes get damaged by ectoparasites. Worn and damaged feathers cannot function well and this can prove fatal if the bird cannot fly properly.

As feathers are dead structures, they need to be replaced regularly. And this process is known as moulting. In moulting, the growth of the new feather pushes out the old from its follicle.

Moulting may be partial or complete. Partial moult occurs when only certain feathers or groups of feathers are replaced. Complete moult occurs when all the feathers are replaced. Thus when birds develop their winter plumage or change from juvenile to adult plumage, moulting was at work.

The image below is a moulted breast or more likely belly feathers of a Buffy Fish Owl (Ketupa ketupu), picked up below the owl's roost by Melinda Chan. Our field ornithologist Wang Luan Keng has this to say: “Birds do have a season to moult, usually after their breeding season. In Singapore, most birds breed from Feb/March till July/Aug, maybe Sep. Many species here overlap moult and breeding slightly so they will start moulting in July/Aug and end by Oct/Nov when the NE monsoon starts. Many species, especially passerines, have straight forward sequential moult; others like cuckoos, hawks, herons, fruit doves etc have very complicated multiple moult series and yet some species like rails, grebes and probably bitterns moult all feathers at once and go flightless during that period. And mind you, we are only talking mainly about primary feather moult. We know even less about other flight feather moult and almost nothing about body feather moult.”

Input and images by YC; expert information by Wang Luan Keng and owl's feather provided by Melinda Chan.