The odds have it that an accipter carrying a chipmunk in flight is a
Cooper's Hawk. But stranger things have happen.
An observer could easily get a good enough look at a small mammal being
carried by a raptor to know it is a chipmunk. Being positive that the bird
was a small Sharp-shinned Hawk could be problematic.
The smallest diurnal mammals in North American woodlands are chipmunks,
wrote Robert Storer in his 1966 study "Sexual Dimorphism and food habits in
three North American acccipiters."
Storer states that all of the strictly diurnal mammals are well above the
mean prey size of the Sharp-shinned Hawk. The species' diet includes just 3
percent mammals. That almost eliminates a sharpie catching one on the
ground to kill and eat. The foot of a good size woodpecker almost rivals
that of a Sharpie. A small hawk like a Sharp-shinned would generally be
over matched with a chipmunk.
The Cooper's is an entirely diffferent issue.
Storer goes on to report that Cooper's Hawks take considerable prey within
the size range of chipmunks and red squirrels but still feed largely on
birds. Cooper's take about 17.7 percent of their prey as mammals
(15.9-18.9).
A chipmunk being carried by a Sharp-shinned Hawk is probably beyond the lift
capacity of even large Sharp-shinneds in most cases. A small Sharp-shinned
( a male) is the same length and mass as a Blue Jay. Lenghty ~ 11 inches
(Sibley 1990). The weight of a Sharpie is about 5 ounces (140gm) and a Blue
Jay at 3 ounces (85 gm).
The two are roughly the same weight. Don Linzey, "The Mammals of
Virginia," 1998, lists the Eastern Chipmunk at 70-140g (~2.5 ounces to 5
ounces). Sibley, 2000, gives an average of ~ 5 ounces for a Sharp-shinned.
If an observer's first impression was the approaching bird appeared to be
a Ruffed Grouse and it turned out to be an accipter, that would also suggest
a Cooper's. A grouse and a Cooper's Hawk are approximately the same size
and mass. Sibley lists Ruffed Grouse 17 in. and Cooper's Hawk 16.5 in. He
gives the weight of a grouse at at 1.3 pounds (580gm) and a Cooper's at 1.0
pound (450 gm).
Observers can't tell the difference between a Cooper's and Sharp-shinned
under all conditions. It is extremely difficult if not impossible for the
best of expererts in some cases. Frequency and familiarity do not provide
enough skill even for the expert field observers.
Mueller, Berger and Allez (1979) projected great caution with standard
methods of identifying accipters by plumage characteristics: "in
dientifying hawks these are rarely definitive and often misleading." They
believed accipters are among the most difficult of the hawks to identify and
that the identification systems by elimination simply does not work with
hawks. Popular field guides make it look too simple.
They suggest that size is the most reliable key in accipters and research
citied suggests that a Sharp-shinned would not likely carry a chipmunk in
flight but a Cooper's Hawk can and does.
It stands to reason that it would be far more likely a Cooper's than a
Sharp-shinned but stranger things have happened.
Let's go birding....
Wallace Coffey
Bristol, TN
----- Original Message -----
From: "mayhorn" <mayhorn@xxxxxxxxxxxx>
To: "Birding Virginia" <va-bird@xxxxxxxxxxxxx>
Sent: Thursday, March 10, 2005 11:00 AM
Subject: [va-bird] Sharp-shinned gets Chipmunk
VA Birders,saw, what I thought was a grouse, flying low, coming across a large, open
Yesterday (3/9/05) while driving home from Grundy on Rte. 83 my wife and I
Enjoy the birds,email to va-bird@xxxxxxxxxxxxx. To unsubscribe, send email to
Roger Mayhorn
Grundy, VA
Buchanan County
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