Thursday, September 23, 2010

Age and sex ID based on molt, part 1

I take a lot of photographs, and some of the birds I take photos of are as much for plumage interest as aesthetics.  This is an example of a somewhat scruffy Red-winged Blackbird at Brigantine NWR in NJ in August:
Blackbirds go through active molt in August-September and frequently look quite odd.  This particular RWBL has molted some body feathers but not yet the head or neck, so it looks odd in the head.  If we zoom in on the tail:
it is heavily frayed - older feathers not recently molted.
On the wings there's a mix of mostly new flight feathers and one or two older ones:

Looking at the condition and overall coloration of the feathers tells us all we need to determine age and sex, within reasonable bounds.  The feathers on the tail are quite worn, so they are quite a few months old - molted at or around this time last year.  So this bird is an adult, i.e. more than one year old.  Similarly that outermost primary looks pretty worn too.  Since this bird is an adult, the fact that the feathers are brown means that it must be a female - there is no distinct "first summer" plumage for male RWBL birds so a male of this age would have black flight feathers.  In fact the pointedness of that worn outermost primary suggests that this adult female might be only a little more than one year old - flight feathers from first fall passerines are usually more pointed than adults.

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