May 2000 Mystery Birds

Many thanks for the helpful and informative comments. I believe these birds are a Broad-winged Hawk and a Sharp-shinned Hawk.

The Broad-winged Hawk was photographed 6 January 1979 in West Pittsburg, Contra Costa County. It was present 9 December 1978 through 27 March 1979 and was widely seen by many observers including me. Although there are no documented records of Gray Hawk for California, the species has been claimed at least twice and could conceivably occur.

I chose this particular photograph because it seems to show more barring on the leg feathers, and white on the upper tail coverts than typical of Broad-wing. The National Geographic Field Guide (3rd ed.) illustrates juvenile Broad-winged Hawk in flight without any markings on the leggings. Wheeler and Clark's Photographic Guide to North American Raptors also discusses this difference on page 47 stating that Broad-winged differs from Gray in having streaked, not barred, leg feathers, and lacking the white U above tail. This bird seems to me to have barring on the leg feathers and a white U above the tail.

However this bird has just the tips of the uppertail coverts white, not the entire feathers as in Gray Hawk. Also many Broad-wings have barred leg feathers as in this bird. The face pattern is quite variable in the two, and probably not a reliable distinction. I believe the apparent white crescent in the outer wings is a misleading artifact of the photograph which suggests one of the eastern subspecies of Red-shouldered Hawk. Western Red-shouldered Hawks are much more adult-like than they are in the East. The lack of a strong underwing pattern should eliminate eastern Red-shouldered.

The Accipiter was photographed at Point Reyes, 24 September 1980 and identified at the time as a Cooper's Hawk. In 1980, I think birders had more faith in the tail shape differences between Cooper's and Sharp-shinned hawks than they do today. After a landmark study at Golden Gate Raptor Observatory on field identification of known Accipiters, the observatory altered their approach to teaching identification of these birds to their volunteers. They are also routinely taking a measurement of the difference between the longest and outermost rectrices on birds which they band in the Marin Headlands. Sharp-shinned Hawks seldom if ever have all the rectrices the same length and normally show a certain amount of rounding, especially larger females. Cooper's Hawk normally shows more tail rounding at the corners than Sharp-shinned, but this distinction turned out to be rather unreliable in the field in the GGRO study.

The relatively small head and blurry, fairly uniform streaking on the underparts are indicative of Sharp-shinned. Cooper's normally show a more massive head, typically projecting in front of the wings, and crisper finer streaking, more prominent on the breast with the belly lacking much obvious streaking. I agree this bird is best explained as a Sharp-shinned with an unusually high amount of trail rounding. I doubt that the rounded tail is caused by molt, as this is a juvenile photographed in Fall, and all feathers should be the same age.

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