RE: [cobirds] Boulder surprising hawk kill

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: djwaltman@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 <djwaltman@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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