Sharp-shinned & Cooper’s Hawks are 2 of the most mis-identified birds in North America based on their similar markings & structure. The smallest members of the Genus „Accipiter“ in North America, these birds are woodland hawks characterized by long tails & short wings, which aid them in chasing avian prey through dense cover. Some field guides in the past have sought to simplify the ID process by looking for a short cut to ID, by relying on a single characteristic – the shape of the tail, „Is it square or round?“. However, like any tough identification, attempts to oversimplify just lead to confusion & disappointment. Plus, A LOT of misinformed birders making a lot of misidentifications. Separating this duo is recognized as one of the toughest identification challenges in all of American birding, and as such, requires consideration of multiple characteristics as there is overlap in the tail issue, and uneven wear and molt can make square tails round and vice-versa.
Sharp-shinned Hawk (Accipiter striatus) gets its name from its thin, triangular tarsus which are indeed thinner at the front, although most birders will never appreciate this from field views. To be wholly accurate, the tarsus is actually the „foot bone“(the „heel“ would be between the finger & thumb here) and not equivalent to the „shin“. Another poorly-named bird species! Note how comparatively thin the exposed portion of the tarsus and toes are. This can be helpful when separating a Sharp-shinned („Sharpie“) Hawk in the field when perched in a backyard as example.
Juvenile Accipiters are uniformly brown on the back and streaked with uniform vertical brown streaks on their underparts. Raptors show reversed sexual size dimorphism, a fancy term meaning „females are bigger“. This is most prevalent in the American Accipiters & Falcons where the sexes can be as much as 30% different in mass / length. Not likely significant or particularly useful but it does seem the males are more neatly marked and the females a but more blurry. The two above were in the same photo but cut and pasted to be close together for comparison the significant size difference is wholly accurate and unchanged!
Here are two male Sharpies showing plumage differences between ages. After their first complete molt (near one year) Sharp-shinneds (and Cooper’s) replace the brown vertical streaks with reddish-orange, horizontal barring, and the iris color moves from yellow to red.
Seen from behind note the near solidly brown back of the juvenile compared to the cobalt-blue back on the adult. Note too that the juvenile appears longer…. it is! Accipiters have longer tail and flight feathers in juvenal plumage than as adults. Look especially at the comparative lengths of the tails past the upper tail coverts (an important note when it comes to identifying adult male Cooper’s).
While never mentioned in field guides there is a distinct and noticeable difference between colors on adult males vs. females in both of these species. Males are invariably brighter blue and tend to develop a more reddish eye quicker. Females seem to never advance beyond the more gray cast seen above. Both of these birds are in comparatively fresh fall plumage – NOTE how little white is notable on the tail tip! Sharpies will generally show little more than a hint of frosty white here (Coop’s can have a very noticeably broad white tail tip).
Compare the pattern of the streaking on these two Accipiters captured and banded in Cape May, NJ in the fall. The juvenile female Sharpie at right shows a more rounded, compact head and uniform streaking from top to bottom on the underparts. The juvenile male Cooper’s Hawk (Accipiter cooperi) at left shows a distinctly flat, bull-headed look by comparison, and the streaking is distinctly more prevalent up on the breast and much lighter on the belly. In fall this can be even more accentuated by this buffy bloom. As such many times young Coopers will appear to have golden hoods and matching bibs in fall as they fly by.
By spring time any hint of the Cooper’s warm buffy „bib“ has faded away but the streaks are generally still heavier on the breast and lighter to absent on the belly. Note too the flat-topped head, and the more prevalent white spotting on the lower back (compared to a juvenile Sharpie which tends to be uniformly darker backed). Even though partially cut off in this photo, note how the withe tips of the central tail feathers have completely worn off, while those toward the side are still in tact. As such, flying by or perched, this bird would look square or possibly even notch-tailed!!!
This image is not to scale, but note the rounded head on the Sharpie versus the Coop’s flat top. Also note the longer-necked appearance & the contrasting whitish chin on this fall Cooper’s. Often they may show a single dark streak right through the center of this prominent white chin.
As mentioned above, Cooper’s replace the brown vertical streaks with reddish-orange, horizontal barring below. The back changes from brown to bluish-gray, and the iris changes from yellow to red, just like Sharpie. Note that the head still looks bulky and flat on the adult, but more importantly note how the orangish cheek patch (sometimes infused with gray) extends far back on to the neck, wholly separating the dark cap which is always a shade or two darker than the mantle (upper back).
Compare with this adult male Sharpie. Note how the light cheeks are more restricted leaving a complete wide band of color connecting the mantle and crown (which are uniform color, unlike the Coop’s dark cap). Note to the surprisingly thin tarsus here. As stated in the intro it is best to consider a range of features when separating these two very similar species!
Like Sharpies, adult Cooper’s Hawks show a distinct difference in color between male and female plumages. The birds above are a mated pair nesting in suburban Florida. The adult male (right) is in extremely worn plumage in late spring, but is still notably brighter-plumaged than his mate (left) who is mostly freshly plumaged in July. Note the prominent, wide white tail tips on the fresh plumaged female at left. Even though they are near wholly worn off the adult male by a year later, if you see a very prominent white tail tip it’s a very good bet you are NOT dealing with a Sharpie (compare again to the fresh adult Sharpies shown again below).
Even when fresh the whitish tip of the Sharpie’s tail is less prominent and the grayish-brown above blends into the white tip.
Scenario – you’re at a fall hawk watch and a medium-small accipiter races by. You are struck by a deep blue back with an obvious white tail tip, but the bird seems small and short-tailed (unlike the fresh immature Cooper’s that often show obvious rounded tails)… What is it?!?…
Well, it’s the most mis-identified bird of the group, an adult male Cooper’s Hawk! Remember that males & females are very different in size and a male Cooper’s may be closer in size to a female Sharp-shinned than a female Coop. Also remember that adults have shorter wings and tails making the adult, male Cooper’s the smallest looking Cooper’s Hawk of all. Trust that an adult female Sharp-shinned typically appear more brownish-gray appear than bright blue and a wide, white tail tip is really more of a Coop’s thing! Confused?!?… you should be this is a tough ID for a reason, if it makes you feel any better though I once sat on a hawk watch site and watched as the official counter for that day called every single adult male Cooper’s Hawk that passed a Sharp-shinned Hawk. The issue was he had not been doing this as long and did not have the advantage of banding these birds. This allows you to prove definitively through measurements what each bird is after watching it fly in and gives you a finer appreciation of these subtle markings. So never fear even the pros get confused, but hopefully this refresher will help.
Final thought, sometimes birds will show intermediate markings and you may not have all of the characteristics visible (no tail here to consider). In life, characters of size and structure generally ring true, but in a single, still image a bird may be caught in a deceiving position that wasn’t necessarily true to what the bird looked like the rest of the time. E.g. has this bird been captured all stretched out in this image?… or was it briefly adjusting its head feathers the moment the shutter release was depressed?… Let’s open some dialog and discuss this one together as an exercise. You first – add your observations on what you note about this Accipiter. Then once we have a bunch of observations we’ll summarize and conclude with an ID.