Friday, February 12, 2016

Sharp-shinned or Cooper's?

Differentiating Sharp-shinned Hawks from Cooper's Hawks

Sharp-shinned and Cooper's Hawks [Internet Photo]
Differentiating Sharp-shinned from Cooper's Hawks is a problem for the experienced birder.  These species look a lot alike and need careful scrutiny and experience to separate.  They are both members of the Accipiter family, the true hawks.  They are both fast killing machines of mainly birds.  So, their behaviour is similar.  The size of prey can help telling which species it is.  The Cooper's Hawk is larger than the Sharp-shinned Hawk; 36-51 cm compared to 25-36 cm.  The smaller Sharp-shinned preys on small birds.  A robin is often too large for it.  The Cooper's usually preys on larger birds, often doves.  In both species the females are larger than the males.  Looking at the sizes above, you can see that a female Sharp-shinned can be the same size as a male Cooper's.  Since both genders look very much alike, we have to observe fine details closely to tell them apart.

Both species take two years to mature.  The young are generally brownish above and streaked below on a pale background.  The adults are bluish gray above and orange barred below.  Both juveniles and adults have banded wings and tails.  In both species the juveniles are streaked on the breast (streaks run vertically) and the adults have bars on the breast (fine lines running horizontally).  

The Sharp-shinned is more common here.  It nests in mixed forests and is present year round especially in the southern part of the province.  The Cooper's nests further south, preferring broad-leafed forests.  The Cooper's seems to be more common here in winter.  Both species seem to know where the bird feeders are in your area and they check them out regularly for prey.  

Sharp-shinned Hawk Juvenile
The juveniles can be told apart by their streaking.  The Sharp-shinned has 'messy' streaking on its breast; the Cooper's has fine streaking often tear-dropped shaped.  In the Cooper's the streaking is often just on the chest (upper breast) and it covers the whole breast on the Sharp-shinned.  See the breast streaking on the Sharp-shinned pictures above.  The streaks are broad and ill-defined (messy) and the streaks go down to the legs.

Cooper's Hawk Juvenile [Internet Photo]
In the Cooper's Juvenile shown above note the streaking is tear-dropped shaped and is mainly on the upper breast.  Also notice that in both juveniles the colour is brownish on the head and wings.

Sharp-shinned Hawk Adult [Carmella Melanson Photo]
Above is a Sharp-shinned Hawk young adult.  Note that the vertical streaking is changing to the orange horizontal bars of an adult.  Note that the back is still brown and has not changed to the blue gray.

Another help on a perched bird is the finer details of the head.  The head of a Sharp-shinned is rounder than the flatter head of the Cooper's.  The Sharp-shinned has an orange cheek compared to the gray cheek of the male Cooper's (female has orange cheek).  Both have a dark cap but in the Cooper's it contrasts with a paler nape (back of neck) and in the Sharp-shinned the dark cap blends in with the dark nape.  Note these features in the photo below taken from The Sibley Guide to Birds, 2nd edition. 

Note in the photo at the beginning of this post the demarcation of the cap from the nape is not clear enough to differentiate the species.  That is probably because of the lighting in the photo and the head position.

These are very fast birds and we often don't get to see these finer details on birds in flight.  They both fly with the flap-flap-flap-glide characteristic of Accipiters.  The Sharp-shinned, however, has a faster wing-beat than the Cooper's.  They have a similar body shape in flight; long tube-shaped body with long tail and rounded wings.  So, it often comes down to shape and size.

The Cooper's in flight shows the shape of a cross.  The Sharp-shinned in flight has the shape to a 'T'.  The reason for this shape difference is that the Cooper's has proportionately longer wings and the anterior line of the wings is straighter than that of the Sharp-shinned.  That makes the head project further ahead.  The slightly rounded forewing line of the Sharpie and smaller head makes the head appear to be farther back, making the shape of the 'T'.  I have found this is quite helpful in identification.

Tail shape is also helpful in identification.  The Cooper's tail is rounded and has a wider white band on the tip than that of the Sharp-shinned.   The Sharpie tail tip is straight across and has less white on the outermost band.  The straight tail tip of the Sharpie gives it a right-angle on the edge which can be seen sometimes.

Now, what about the shins?  This is a strange identifying feature which goes back to the days when birds were identified by shooting them and mounting the specimens.  When museum specimens are prepared the birds are laid on their backs and thus the shins are very visible.  As you would expect, the shins, or actually the metatarsi, of the Sharp-shinned are 'sharp'.  They are narrow in cross-section with a sharp edge.  The Cooper's has a thicker, sturdier leg.  This feature is not very useful in the field.

This posting may be too detailed for the beginner naturalist.  It is, however, the 'stuff' experienced birders have to consider in order to identify some of our difficult species.  It all depends on the quality of the view we have, whether the bird is perched or in flight and how long we are privileged to have the bird in our sight.

Good birding, all!

References: Sibley, David Allen. The Sibley Guide to Birds. 2nd edition. Knopf, Borzoi Books. 2000.

Cooper's and Sharp-shinned Hawks. Alvaro Jaramillo. In Bird Watchers Digest. Vol 38 No 1. Sept/Oct 2015.

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