Posted by: atowhee | August 10, 2016

CONFUSION: MAYBE NOT SO SHARP

AUG. 31, HERE is what seems to me to be a definitive analysis of this series of photos from Mathew Hunter.

“Sorry for the delay; life’s been busy!  Accipiters are HARD sometimes. I’d like to share my thought process….

1. My first impressions were of little doubt this was a Sharp-shinned Hawk (SSHA). The wing shape against the fence looks typical SSHA, short, wide, angled. The head looks small. The legs look really wire thin. The heavy barring is more typical of SSHA.  However, a fence like this where I live is typically just under 4 ft tall, so that wire spacing would be 3 or so inches, making this a larger bird. Hmmmm.

So, let’s dive in for more analysis…

2. What is the age of this bird? What do we see? (According to photographer, photo taken about August 1st in Rocky Point area at Klamath Lake.)

(a) The underparts: They are not the thin streaks of a hatch year (HY) Cooper’s Hawk. They are not the fine barring of an adult of either species. We don’t see the actual breast and belly very well in any of the photos, but we can see it best in the second photo, where the bird is flying left with its legs out of the way. Here we can see that there are in fact fairly wide, reddish longitudinal streaks. It is common for immatures of both species to have barring versus streaking on their leg coverings, and at the sides of the breast and belly. The pattern here is of a non-adult bird.
(b) The back: the scapulars especially, have pale spots (see bottom photo). Although some adults or sub-adults can have some pale spotting sometimes, this is more characteristic of non-adults. Hard to discern color or be certain about feather edgings.

(c) The tail appears long with many well-defined dark bars. Immatures of both species tend to have longer tails and more visible bars that are more sharply defined than in adults. The tail shows these non-adult characteristics.

(d) The face, is hard to see clearly, but appears to have a slight eyeline and certainly has quit a bit of dull streaking so that there is not much contrast between the cap and face. This is consistent with a juv or imm or subadult bird.
(e) The eye: in shaded settings with poor light/exposure such as this, an adult red eye typically looks dark. These photos clearly show a quite pale iris that looks yellowish on my screen; but the point is that the iris is quite pale, a non-adult characteristic for sharpy or coop.
(f) All features point to a non-adult bird. If the bird is this-year’s bird, then it has to be a Sharp-shinned Hawk, because juvenile Cooper’s Hawks never have that heavy and wide of barring, and reddish-brown barring at that, on the underparts, whereas Sharp-shinned can have (and frequently does have) such wide barring.  Could this be a 1-year old bird? Well, if it were 1 yr old in early August, it would most likely show some evidence of wear and molt. Not sure that photos are adequate to address wear, though what feathers are fairly clear appear to have nice smooth edges. I don’t see any evidence of molt in the flight feathers. The outer tail feathers appear messed up, and in last photo a short primary and the alula are out of place; hard to know if this is because of the encounter with the fence….  Awkward fence encounter suggests young bird.

3. The tip of the tail is a bit hard to discern, but based on the appearance with both backlighting and shadow, it appears that distal from the last dark bar, there is an area of gray, and then a very thin white tip. With backlighting, the gray and white together look like they could be a wide pale tip, like on Cooper’s Hawk; however, the pale tip in the backlit photo with tail spread appears similar in color to the pale bars on the rest of the tail (in coop it would be notably whiter). In shadow, the tip of the tail shows a mostly dull color past the last dark bar, then a very thin pale edge. This is consistent with juv Sharp-shinned Hawk tail feathers.
4. Now, let’s look at that fence as a reference for measurements. The original observer measured the fence wires at 2″ spacing horizontal and vertical. Note that if the bird is any significant distance towards the camera from the fence, our length estimates will be overestimates, higher than actual. Thus, measurements from the first photo are likely to be fairly accurate as the bird is right on the fence; whereas in the second and third photos, the bird is in flight perhaps 1-3 ft in front of the fence and measurements from those photos may be slightly higher than actual.

(a) Wheeler and Clark (North American Raptors) give length measurements defined as from the top of the head to the tip of the tail (slightly different than museum measurements). The first photo appears to show the bird taking up about 6 vertical spaces. This would translate to 2″ x 6 = 12″ in length. Wheeler and Clark give length measurements of 9-11 for male and 11-13 inches for female Sharp-shinned Hawks; and 14-16 inches for male and 16-19 inches for female Cooper’s Hawks. Our estimate falls in the range of female Sharp-shinned Hawk.

(b) Wing span on first photo appears to be about 24 inches. Wheeler and Clark report 20-22 inches for male and 23-26 for female Sharp-shinned Hawks; and 28-30 inches for male and 31-34 inches for female Cooper’s Hawks. Our measurement again falls in range of female Sharp-shinned Hawk.

(c) Wing chord is the distance from the front of the bent wing to the tip of the longest primary. With all the angles it is difficult to determine, but in the 2nd photo, I would estimate a wing chord of about 4-4.5 squares or 8-9 inches. From the third photo, the wing chord looks again to be about 4-4.5 squares, or 8-9 inches. BNA gives average measurements of males in Michigan ave 6.72 inches, females 7.9 inches; and roughly similar measures for breeding birds in Oregon. For Cooper’s Hawk, 8.9 inches for males and 10 inches for females. This test is inconclusive (and figures are only averages, not ranges). However, as previously explained, our estimates from this photo would be higher than actual, which would shove the real-life measurements lower, again toward a female Sharp-shinned Hawk.

Well, that’s what I see. 🙂

Matt Hunter”

Here is an accipiter trying to cope with the real world and one of its more confusing elements, a fence.  Millions of years of evolution did not prepare this bird for this obstacle.  COOP FENC1 COOP FENC2 COOP FENC3 COOP FENC4

 

These photos were shared by Shannon Rio and her husband, Kirk.  Here’s her explanation: “Kirk and I were sitting on our cabin porch [near Klamath Lake] and he spotted this coopers.  It seemed confused by the fence.  It could not get over this low fence.  I kept quietly telling it that it is a coopers hawk, a slender agile mobile hawk that can slink thru anywhere but this young kid just was not interested in the ramblings of an older woman.  Finally it hopped onto the top of the fence and took off.  It was at the base of some shrubs that are the apex of major yellow warbling sounds.  So, ok, about a half hour later, Kirk spots a Cooper in a nearby tree and then it is gone.  Then a young yellow warbler goes to the top of the shrub and gives pathetic calls for quite a while.  We were wondering where the coopers hawk was but perhaps it was full.  Anyway, that is our story.  Another day in bird paradise.”

 

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Responses

  1. I’d say coops by the tail. It’s flared and distinctly coops. Ask for the fence wire dimensions, that will help with size. I think it’s basically on the fence wire (in the first pic) so count the squares to find out the birds length.

  2. I liked the comment on forehead to bill to compare, and it is always fun to add another element to the features of these species in analysis.


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