Molting Icterids

Blackbirds are notorious for looking absurdly messy at this time of the year, losing large chunks of tail and body feathers as they undergo prebasic molt into non-breeding plumage. Blackbird flocks are often quite shy, but this bird popped up long enough to grab a few shots. It's in very active molt with most body feathers freshly replaced, except the head which is just starting to molt. That's why the neck looks odd. The tail feathers are heavily worn adult feathers - very frayed at the ends. On the wings the secondaries are fresh and clean, but some primaries are still adult and yet to be molted in.

All sorts of things are going on with the plumage of this bird. That's one of the things that photography has improved my appreciation of - aging and sexing birds by feather age and structure, as opposed to just plumage color. This picture was taken on August 28th 2010 at the Brigantine Division of Forsythe NWR.

In this case it's not too difficult, since we can easily age the older feathers by fraying. (An alternative would be by shape since juvenile feathers are more pointed). Since they are heavily frayed in August this bird must be an adult (a bird born this past summer would not have this level of wear - it's feathers would be in good condition). The tail feathers in particular are very heavily worn. They are also brown, so these adult feathers belong to a female - the vast majority of birds molt flight feathers once, each fall, so these feathers are about a year old.




Over on the wing, there's a mix of fresh feathers and worn ones. The secondaries and some of the primaries appear to have been replaced, with at least one worn primary left from last year's molt. Ducks replace all their primaries at once, rendering them flightless for a while, but most other birds including passerines replace feathers in a more controlled stepwise approach.

And there you have it - not the prettiest bird in the freshest of plumage, but it speaks volumes about molt strategies.

There is also a difference in primary shape between the more pointed older feather and the more rounded new ones. This might be a difference between definitive basic and juvenile flight feathers (i.e. this bird is a little more than 1 year old), or this might just be a difference in feather structure due to position.




Update: on Sept 6th at Brigantine at least some Red-winged Blackbirds appeared mostly tailless, suggesting that their retrices were in active molt.