Gosper's Hawk (Was Gull ID Query)

[Greg Sargeant]

While in Galilee this afternoon I happened upon a gull by the side of the road that I had trouble identifying. Luckily I had my camera handy and was able to snap this picture:



My first impression was that it was a GBBG, and in the picture some of the feathers do look slaty-colored rather than the bluish-gray of a Herring. But there is no gonyedal spot evident. Any ideas?

[cwl50?]

Glad you had your cam! Nice shot Greg

[Jim B]

Well, looking at the white mirrors on P-9 and P-10 and the contrast between the upper wing and wingtip I'm leaning towards Lesser Black-backed Gull. Clearly this is a gull identification problem that we failed to cover in all of last year's gull study. I think we should put the question before our good friends at Massbird. What do you think?

[Greg Sargeant]

I'm inclined to agree, based upon the yellow iris, the markings on the bill and the presence of immature coverlets. I'm assuming the gonyedal spot fades after death, since it isn't apparent in the photo. I first thought GBBG but now that you mention it, it looks good for a 2nd winter LBBG if Olsen and Larsson are to be believed.

How about the accipiter? Cooper's or Goshawk?

[Jim B]

OH ! There's an accipiter there?


I admit that my initial reaction was Coopers and I then went to work on the gull. Then Tom C. whose opinion on raptors I value highly chided:

"that accipitor has rectangular streaking from head to legs
[actually on the leggings too]. The streaking pattern doesn't
diminish downward. Even on the belly, each brown streak marking is
the same width top/bottom These brown markings are not teardrops at
all, are they?

While the tail looks long, the outer feather, on our left as we get a
good look at the slightly flaired undertail, is essentially the same
length as the next feather in..."

I thought the streaking looked teardropped but Tom makes an argument for sharpie. Looking closely it looks like more than a hint of yellow skin on the supraorbital ridge. Compare Wheelers Plate 167 and Plate 187

[Greg Sargeant]

It was definitely too big to be a Sharpie.

Here are a few more pics:



Front view of the head. Someone mentioned that pure white underwing coverlets would indicate a Cooper's. Someone else mentioned the extent of spotting on the legs would indicate it was a Goshawk



Profile of the head. The bold supercilium stripe is a typical Goshawk trait but is not uncommon in Cooper's either. There seems to be an auricular patch and malar stripe as well as a facial ring, which are Goshawk traits (according to Wheeler). Cooper's faces should be more uniform (Wheeler) .The tail bars look strait, not uneven which would lead one to believe it was a Cooper's



This is the picture that shows the upper side of the tail. Although the picture is blurry, if you look hard enough you can see thin white edges around some of the black bands on the tail, a Goshawk trait rarely seen in Cooper's (Wheeler again).

[Jim B]

You have a point ! Perhaps I misinterpreted Tom's intent.

[Greg Sargeant]

The red arrow points to the gull's eye.

The case for Northern Goshawk:

White supercilium stripe widening towards the back
Auricualr patch
Malar mark
Whitening at the back of the head
White bars on the upper wings
Thin white edges on some black tail bands
Extensive marking on the leg feathers
The under tail coverlets are not completely white
It's eating a gull for lunch.

The case for Cooper's

Too brown, Goshawks are usually more grayish
Not stocky enough to be a Goshawk
Looks too small
Undertail coverlets are white
Tail is too long
Tail bars are too even

I have to say the opinions seem to be about 2/3 in favor of Cooper's. Tthe points they make are weaker than those in the N. Goshawk camp, however. One person has suggested hybridization, and Jim thinks its a Sharpie on a Ring-Billed.

[Greg Sargeant]

Well it appears as I was right all along (except when I was convinced it was a Goshawk)!!! I posted these pictures at a couple different sites and to the RIBIRDs list and, to Frontiers of Identification. Weighing the evidence didn't seem to do much good so I am relying on the opinions of other birders. Most felt that this was an especially problematic ID regardless of which conclusion they reached. It was neck and neck as far as opinions were concerned. 12 respondants favored Goshawk and 14 favored Cooper's. Many birders whose expertise is hawks were certain that this was a Cooper's. What really tipped the scales in favor of Cooper's is that a team of observers conducting the South County CBC had seen this same bird (apparently) in Galilee a few days earliar, and after concluding it was a Cooper's went back to double check that it wasn't a Goshawk. The structure of the tail bars is, apparently, too straight/even to be a Goshawk. This was mentioned by several others as well. The Goshawk traits, while not necessarily common in Cooper's Hawks, are not rare either.

Another factor in the ID is the size of the gull. The gull was a second year Herring from the looks of the carcass which I relocated yesterday afternoon. The carcass was in poor condition, missing its head. Based upon the remains that I was able to measure and comparing the length to the photos I estimate that the hawk is about 18-20 inches long. This would be about the maximum length for female Cooper's and the minimum length for male Northern Goshawks.

I have to say this exercise has been very interesting and I have learned a whole lot about juvenile accipiter identification in the process. Thanks to everybody for their opinions on the subject and help with ID.

[veery]

Greg, could you repost your photo to the Photos and Art forum? We could compare it to the young Cooper's Hawk that PI Birder posted there today.

[Greg Sargeant]

I can't seem to post onto that thread and keep getting a DEBUG error message

[Jim B]

The DEBUG ERROR message has been, well, debugged. Just in case it happens again, you can ignore it. Your post goes through anyway. Sorry about that.