Thursday, September 2, 2010

Oh, oh... Molt again

Great-tailed GrackleGreat-tailed Grackle, Hines, Oregon on 23 May 2009 by Greg Gillson.


Recently I was working through some photos from last year. Usually, after a photo shoot, I will immediately turn the best RAW shots into jpeg's and post those. Then, as I have time, I will work on the other shots and delete the (numerous) bad ones.

So, for instance, when I photographed this vagrant Great-tailed Grackle in the parking lot of a restaurant in Hines, Oregon, 15 months ago, I uploaded the best shot immediately. That left me with some shots like this one, above, that I am finally getting back to.

Even though I pulled the lens in from 400mm to 340mm it was not enough, as the bird was so close. As a result, the entire tail didn't quite make it into the frame. And there's this distracting yellow "something" pointing right at the bird's head. So, it is not a very artistic photo.

However, it shows something that I didn't realize at the time. This bird is almost exactly one year old. How can I tell? Molt limits.

Now I've been birding 38 years, and am just "getting into" understanding molt. So I sympathize completely if you don't find this as interesting as I do right now.

For most birders,... the brain fogs over at the mention of molt. -- Alderfer and Dunn, National Geographic Birding Essentials, 2007.

Last month I discussed this topic using a photo of a juvenile Brewer's Blackbird in molt. Today's post continues that discussion.

Even though this is a black bird, it is not completely one solid black color. Much of the plumage is rich black with glossy purple and green iridescence. However, many feathers on the wing and tail are dull brown.

Those dull brown feathers are retained juvenile feathers. Those are the first feathers this bird ever grew, probably in June of the previous year. Now, in the month of May, 12 months later, those original wing and tail feathers are quite worn. They contrast quite nicely with the glossy black feathers that were part of the pre-basic molt in the previous September.

In the next fall (2009) this bird will molt in new wing and tail feathers (and all feathers, actually) and be in definitive basic plumage. From then on, all through its life, it will undergo a complete molt each fall. Only during this first year and a half, can the age of this species be determined using molt limits.

Knowing the age of the bird tells us something about this vagrant. Even though this species is expanding its range, this young bird wasn't likely to be breeding this year. If it survives, it will likely migrate back south for the winter and possibly remain south to breed the next year (spring 2010).