Most birders know how to tell 1st-year (juvenile) Bald Eagles, but some 3rd and 4th-year Bald Eagles (and some 2nd-years) appear dark-bellied and dark headed in the sky and can be tricky to tell from 1st-years. So, what do you look for on dark-bellied Bald Eagles overhead? One of the neatest things to look for are the "translucent" tips of the inner primaries that appear as if 1st-year birds are missing feathers. Older birds may have white on the inner primaries, but the tips of the feather are black, so the wings lack the "missing feather" look of 1st-years.
Also, when 1st-year birds bank in the distance and reveal the upperside, the overall tone to the topside is helpful. Of course most 2nd and 3rd-year birds have a white patch on the upper back, but many 3rd and especially 4th-year birds lack an obvious white patch. However, they also lack the two-toned upperside (evenly brown upperwing coverts contrasting the blackish flight feathers - that becomes very obvious by winter) that 1st-year birds show, instead having a darker overall topside. 2nd, 3rd, and especially 4th-year Bald Eagles may show faint to obvious white on the top of the head, juveniles always show dark heads (but some have white on the throat).
Check out these 1st-year birds on top (and bottom right - upperside photo) compared to the 3rd-year birds on the bottom. And remember, of course no field mark is 100% accurate, there are exceptions to every rule!
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12 Comments:
Interesting, the juveniles do look like they have a missing feather. That's a neat tip Jerry, thank you as always for sharing your knowledge.
Thanks for checking in Daniel.
I can't tell you how many times I've heard people ageing Bald Eagles based on body color alone, 2nd, 3rd or 4th year. Then someone notes 'it must be molting, some of the wing feathers are missing'. The bird is really a juvie like you pointed out. Thanks Jerry for making that clear for us.
Thanks Derek....glad you noticed this too!
Excellent ID tip Jerry!! And superb photos to illustrate it!!!
Thanks Vic:
I just see this 1st-year/3rd-year issue often at hawk watches and thought I would try to simplify it. I think it is useful.
Interesting tid-bit...I'm alaways looking to learn tid-bits like this. Thanks for sharing.
Wow, the translucent/missing feather look is a really great way to ID the first year birds. Great tid-bit, Jerry. It does get a little tougher after that to narrow down the 2nds 3rds and 4rths unless in the latter you start seeing some white, sub-adult feathers on the head and rump/tail.
Jerry, do you know how many molts it typically takes to develop the complete white? I know it varies, but a guestimate? I know it must take at east 2, but could it take more and does it usually?
It takes about 5 molts to get the complete white head and tail and complete black body, sometimes longer...but by complete I mean zero leftover remains of any sub-adult plumage markings. And, it varies by population and individually.
Yes, thank you that's what I meant, complete. Because how often do you hear people observing a sub-adult and saying "she's a 4 year-old because you can still see some dark feathers in that white. Next year she'll have a full white head and tail"? I hear it that a lot and it's not exactly 100% correct. It's reached adult-hood and sexual maturity, but it hasn't exactly developed it's full and complete white head and tail by its 5th year.
And along the lines of populations that you mentioned, that transformation to complete white is most likely different in the darker and larger birds in the northern parts of NA and Alaska than the southern lighter ones in areas such as Florida and such.
On a related note, I just learned from this blog about the fading of feathers which I've seen but never really noticed or paid enough attention to. What causes that pigment to fade? Sun exposure is my first guess or is it climate? Or just a natural occurrence that's not really related to anything in particular?
You are right on the $ with those comments. Sun is the biggest factor in fading plumage, wear is contributing
Thx, Jerry. So much to learn, so little time....:)
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