I wonder if the increased numbers of Cooper's Hawks is a reason for the
decline of both Sharp-shinned Hawks and American Kestrels. I presume
the kestrel numbers have declined over the years do to a few things, one
being trichinosis, but are Cooper's Hawks taking their toll on these
little raptors as well?
Scott Rashid
Estes Park
On 2/27/2015 11:37 AM, William H Kaempfer wrote:
Nick,
I went to CBC data for Colorado to see what it says. From the early
1990s up through about 2005 or 2006 both Sharp-shinned and Cooper’s
Hawk numbers increased steadily: up 125% for Sharp-shinned and 135%
for Coopers. Since then, however, Sharp-shinned have gone back to
about where they were while Coopers have doubled again. During the
period from the 91^st CBC (which if I recall means the actual end year
is one before, so 1989-90) to the 105^th CBC, Cooper’s numbers grew
fairly steadily from just under .01 per party hour to just over .02.
in 15 years. But then things really took off, for every year since
count number 106, Cooper’s Hawk counts have been between .03 and .04
with a high of .0418 on the 111^th count.
What about Eurasian Collared-Doves? Their numbers have grown 12 fold
in the last decade. My conclusion is that Cooper’s Hawks are an even
greater beneficiary of all of that food source that is now available
and they are prospering. But, more Cooper’s Hawks might mean fewer
Sharp-shinned Hawks.
Bill Kaempfer
Boulder
*From:*cobirds@googlegroups.com [mailto:cobirds@googlegroups.com] *On
Behalf Of *Nick Komar
*Sent:* Friday, February 27, 2015 10:05 AM
*To:* djwalt...@comcast.net
*Cc:* cobirds
*Subject:* Re: [cobirds] Boulder surprising hawk kill
Sharpies take Eurasian Collared-Doves on a regular basis. The dove is
almost 50% larger than the hawk by mass. This brings up a question:
why are there not more Sharp-shinned Hawks around? There must be more
influential constraints on the hawks population than winter food
supply. Any thoughts on what those constraints might be?
Nick Komar
Fort Collins CO
Sent from my iPhone
On Feb 27, 2015, at 9:29 AM, David Waltman <djwalt...@comcast.net
<mailto:djwalt...@comcast.net>> wrote:
I just witnessed a Sharp-shinned Hawk successfully kill a
Steller's Jay. It's sitting on the ground eating the jay right
now. The Steller's Jay is about the same size as the
hawk, although the Sharp-shinned would outweigh the jay at about 5
oz. vs.3.7 oz. I'm amazed that a Sharp-shinned Hawk would go for
a bird that large.
David Waltman
Boulder County foothills, 1/2 between Boulder and Lyons
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