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Hawk watchers beware

posted by Jerry Liguori at
on Saturday, December 18, 2010 


One of the trickiest aspects of hawk identification is ageing and sexing "brown" (adult female and juvenile) harriers at a distance. Most people are familiar with the rusty colored, essentially unmarked underbody of juveniles versus the paler buffy, streaked underbody of adult females. However, adult females can show rusty undersides (more common in the West) and appear very similar to juveniles, and the underside of juveniles fades to buffy by late fall and appears similar to that of an adult female.

Before "clicking" on the composite above to enlarge it, note the overall color of the 4 birds as they would appear in the field. The 2 left-hand birds appear orangey underneath as you would see on typical juveniles, and the 2 right-hand birds appear buffy resembling adult females. Now enlarge the photo and see that the 2 adult females (1st and 3rd bird from Utah, November) show streaking on the body, and the 2 juveniles are basically unmarked on the body. The 2nd bird was photographed in September and the faded juvenile (last bird) was photographed in December in Utah. Consider that, if the lightly marked adult female was an orangey type, it would be nearly impossible to tell from a juvenile without ideal views.

Yes, there are other plumage differences between adult female and juvenile Northern Harriers (topside color, marked undertail coverts, head pattern, etc.), but they are minor and difficult to pick out without considerable experience. Telling Harriers from other hawks can be difficult alone, so classifying a "brown" Harrier as unknown age/sex shouldn't be a bother.

Happy Hawk watching,
Jerry Liguori

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9 Comments:
Blogger CarlIngwell said...

Jerry, awesome post. No one writes better advice on how to age/sex raptors & I mean that.

December 20, 2010 at 9:22 AM  
Blogger Tim Avery said...

Jerry,

At what point do juvenile Harriers obtain adult plumage? Bird 4 is picking up streaking at the base of the neck, so I would assume that the transition happens at in the spring, and this bird is just beginning to pick up those adult markings?

I have never really looked closely at Harriers to differentiate and/or sex females v.s. juveniles, but after reading this I will certainly take not going forward.

Thanks for another great post!

December 20, 2010 at 10:08 AM  
Anonymous Jerry Liguori said...

Good question Tim.

Juvenile Harriers start their first molt in April (some very late March, some early May) and that is when they begin to acquire adult plumage. Almost all juveniles have some streaking on the sides of the breast, but it is faint to somewhat noticeable (but never at a distance). I used the words "essentially unmarked" in the post to describe the underbody of juveniles because 9 out of 10 times a birder would never see the streaks. Although nowadays with the capabilities of digital photography, you can see lots of up-close photos of juvenile Harriers.

Glad you liked the post, I have a lot more to come if the feedback warrants it.
Jerry

December 20, 2010 at 2:25 PM  
Blogger Tim Avery said...

Ah, good to know. Keep them coming!!! It's good stuff.

December 20, 2010 at 3:59 PM  
Blogger Just My Take said...

Jerry,
What about molt in the remiges? When do juvenile harriers molt their flight feathers for the first time? Are adult females in active wing molt during migration (spring and/or fall)? I notice in bird #1 that their appears to be active wing molt and bird #3 shows paler inner primaries. Is this an indication of feather age or is this typical of an adult female harrier? I've done a lot of hawkwatching but I tend to focus more on gestalt (and finding the damn flight line) than on plumage subtleties but this is helping to pique my interest.

December 21, 2010 at 11:32 AM  
Anonymous Jerry Liguori said...

Juvenile Harriers start their first flight feather molt at about one year old (typically April). They usually undergo a complete flight feather molt this first time around, unlike many other large raptors that tend to retain a few primaries, or primaries and secondaries. Yes, bird #1 still has a secondary nearly grown in. The paler inner primaries on bird #3 are because the dark terminal band is less prominent on the inner primaries compared to the secondaries on all harriers. You can see it in bird #2 as well (juvenile), and this is extremely obvious on adult males because they are so white underneath.

Hope this helps,
Jerry

December 21, 2010 at 3:06 PM  
Anonymous Kerry Ross said...

Great article Jerry. Short and concise. I look forward to reading others. Thank you or sharing your knowledge with us.

December 22, 2010 at 10:15 AM  
Blogger Ryan O'Donnell said...

Great topic, thanks for posting!

January 3, 2011 at 10:39 AM  
Anonymous Jerry Liguori said...

Glad everyone liked it

Jerry

January 3, 2011 at 11:28 AM  

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