If you aren’t a song expert – and even if you are, you probably have some trouble with female and immature birds – many people are caught out by them. Also, in fall for some birds there is a period called an ” eclipse.” During this period, male birds cast off their flashy breeding plumage and come to look a lot like the females.
This female-like plumage is held very briefly by ducks and other birds in late summer and early fall, and is most noticeable in the males. Eclipse is really the basic or winter plumage, but is worn in summer by most ducks, except the Ruddy Duck which wears eclipse to late winter. Most ducks acquire breeding plumage in the fall, six or seven months before other birds.
I was caught off guard once, (before I learned of eclipses) by what looked like a half-male half-female wood duck – which turned out to be a male in eclipse.
For somebody who didn’t know much about females and immatures, they could have serious problems in the late summer and fall, because in the spring they say: “Why look at a brownish female Yellow-rumped Warbler when you can instead look at the obvious, snazzy male singing away in that that tree?”
An understanding of molting patterns can be a useful aid in identifying many species and in determining their age. Birds need to molt their feathers at certain intervals in order to preserve the structure needed in flight. Molting also can change a bird’s plumage, such as changing from breeding to winter. Very large birds, such as eagles and pelicans, can have complex, irregular molts that last for months. Most birds, however, have regular, predictable molts that occur usually over a few weeks during a period when they are not nesting or migrating.
For those who are interested in learning more about molting, Molt in North American birds by Steve N. G. Howell explains it in four strategies: simple basic, complex basic, simple alternate, and complex alternate.
So get those females and immatures learnt in spring, so that later you’re ready.
In later posts on this subject, I will continue with more on molting and eclipse plumage, and look at some other examples.