It’s that time of year again, just as we humans are gearing up for a (hopefully) great summer, it is about all over for most breeding birds and autumn is on the way. This is particularly noticeable in wildfowl, as they start their post breeding moult in June and July.
Wildfowl – Family Anatidae (ducks, geese and swans), have an interesting moult strategy, unlike most other bird species which moult their primaries (flight feathers) sequentially. This means in most birds, only one feather is dropped at a time, with the new one growing (mostly) out before the next in the sequence is dropped. The Anatidae however, moult their primaries simultaneously, dropping all of them at once. This of course, renders them flightless for a period of a few weeks, whilst their new primaries grow out.
A strange strategy you may think? However, this is where eclipse plumage comes in. Many species of duck are strongly sexually dimorphic – the males and females have different plumages. During this flightless period, the brightly coloured and patterned males of some species would be susceptible to a higher risk of predation, therefore they moult into a plumage that resembles females and juveniles, to camouflage them more effectively from would be predators. This plumage is known as eclipse.
Observation of a group of drakes in eclipse can reveal some strange and interesting looking birds!
When all the primaries are replaced, males once again moult into their bright colouration and look stunning in fresh plumage. Look closely at male ducks in late September, October and November and you will notice that they look pristine!