Boulder surprising hawk kill

[David Waltman]

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

[Nick Komar]

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

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[The "Nunn Guy"]

Similarly, our "little" but ferocious Merlin takes out our fat Eurasian-collared Doves all the time.

Thanks Gary Lefko, Nunn
http://coloradobirder.ning.com/
Mobile:  http://coloradobirder.ning.com/m

[DAVID A LEATHERMAN]

Neglected sending this to the whole group, as intended.
Dave

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From: daleat...@msn.com
To: quet...@comcast.net
Subject: RE: [cobirds] Boulder surprising hawk kill
Date: Fri, 27 Feb 2015 10:28:38 -0700

David, Nick, Gary, et al,
Interesting observations, all.  I would throw in seeing a Northern Pygmy-Owl fly past with a Steller's Jay in its talons one time in Rist Canyon west of Fort Collins.  The owl is 2.5 oz (70g), the jay 3.7 (105g).  The literature talks about a pygmy-owl that was threatening a Dusky Grouse (1050g) , but that report was unclear as to whether it was a predator-prey thing or territorial harassment thing.  For sure, hunger and brood protection are both strong motivators.

As for Sharp-shin numbers, I was always under the impression the majority migrate south.  Maybe how many stick around is somehow driven by autumn weather and the sudden cold snap we had in early November made up the minds of  birds sitting on the fence, so to speak.  Sort of like kestrels, Great Blue Herons, meadowlarks and other semi-hardy species that we have a few of in winter, but not in bulk.  Just a thought.

Dave Leatherman
Fort Collins

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Subject: Re: [cobirds] Boulder surprising hawk kill
From: quet...@comcast.net
Date: Fri, 27 Feb 2015 10:04:41 -0700
CC: cob...@googlegroups.com
To: djwa...@comcast.net

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[Leon Bright]

COBirders,

One late spring a few years ago at our cabin in western Custer County (9,200 ft.) I witnessed an interesting episode involving a young Sharp-shinned Hawk.  I was watching a group of small passerines on my platform feeder when I saw them scatter in a panic.  I noticed a sharpie had just landed on a fence post close by.  After a while he (probable gender) left, and three Steller’s Jays came to the feeder.  The sharpie returned to the post.  The jays didn’t fly off but were very nervous, jumping and flitting around.  The hawk made a couple of feints and the jays left reluctantly.  With no prey in sight, the Sharpie left again.  A couple of hours later there were several Band-tailed Pigeons feeding when the hawk showed up again on the fence post.  The pigeons completely ignored the accipiter which, even though inexperienced, decided against any try at prey whose 13 ounces outweighed his five or less.  He left for the third time, not to return at least to my knowledge.

Leon Bright, Pueblo

[William H Kaempfer]

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: cob...@googlegroups.com [mailto:cob...@googlegroups.com] On Behalf Of Nick Komar
Sent: Friday, February 27, 2015 10:05 AM
To: djwa...@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?

To view this discussion on the web visit https://groups.google.com/d/msgid/cobirds/B0E4A4EC-CA16-4E08-9211-1A840FEA3DBB%40comcast.net.

[Casey Setash]

Having worked on the Cape May Raptor Banding Project this past fall, I had many discussions with a variety of people about the diminishing Sharpie populations.  It's been a noticeable trend in the capture data and the hawkwatch count data that Sharpies have been decreasing steadily over the last decade or so while Cooper's Hawks have been steadily increasing.  One of the major theories for this among everyone I talked to was the increasing fragmentation of forested habitat.  It might be that Sharpies are more reliant on dense vegetation and canopy cover to catch their unwitting prey, while Coops have been able to adapt to an increasingly urbanized environment.  This is just a theory and I'd be interested to see whether any data has been collected to back this up, but there has definitely been a noticeable shift in the proportions of these two Accipiters in the east.  That being said, we did have Sharpies make multiple passes at the pigeons we used as lure birds.  They commonly landed on starlings (even the tiny males would go for a starling), but I believe we only ever had one female land on a pigeon long enough for us to trap her.  There was a relatively recent discussion on the weight-carrying capacity of Sharpies on the CFO Facebook page if anyone is interested.  

Good birding,

Casey Setash

Fort Collins

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Casey Setash

Vice President, VT Student

Chapter of The Wildlife Society

Wildlife Science

Virginia Tech Class of 2014

[scott]

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

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