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Not a pitfall, but interesting Part 2

posted by Jerry Liguori at
on Wednesday, November 2, 2011 


About the Red-tail I posted a few days ago; most people wondered if it was a plumage thing I was alluding to, its not....its actually a lack of something specific I was getting at. The interesting thing about the bird is that it has a complete set of flight feathers (wings and tail) that are all from this year's molt (summer/early fall molt). Basically, they are all the same age without any flight feathers retained from the previous year. This is not extremely rare, but it is definitely uncommon on Western Red-tails in particular. Most Red-tailed Hawks and larger birds in general, retain a few outer primaries and often a few secondaries (to a lesser extent, tail feathers) in their first adult plumage. What would be ultra rare is to see one set of completely replaced flight feathers on an older adult.

The birds above ("click" to enlarge) show a Red-tail in its first adult plumage (left), and one that has at least molted twice (right). The bird on the left shows retained juvenile primary 7-10 (paler due to fade, lacks the bold banding of the adult primaries), and retained juvenile secondaries 3 and 4 (paler, and the black band at the tip is narrower than the adult feathers). The bird on the right has two ages of adult feathers (all the same pattern but the retained adult feathers from the previous year are faded). Note the eye color on the birds above, the pale-eyed bird is the younger adult (left), the dark-eyed bird is older (right). This is not always accurate for ageing birds on its own, but it a good indicator in most cases.

The bird from the other day lacks any age difference in the flight feathers, they are all new feathers that lack any wear or fade. Obviously, this can be difficult to see in the field, but often it is easy to see on clear photos. Anyway, just thought I would share that.

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2 Comments:
Anonymous Drew said...

Oh, you wanted us to look THAT close.... I missed that. Any ideas what would cause a complete molt like that?

November 7, 2011 at 4:39 PM  
Anonymous Jerry Liguori said...

Probably a short-distance migrant or non-migrant that was healthy and has the time and energy to complete its molt. Longer distance migrant RT's and higher elevation RT's tend to lag in molt compared to birds that do not move, move only a short distance, or are from warmer, lower climates.

November 7, 2011 at 6:18 PM  

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