Hi, Roy -
I agree with Larry, and have some observations and logic to add. Most juvenile
raptors (possibly excluding ones with extended family cohesion - e.g. Harris.s
Hawk, Galapagos Hawk) get a few weeks to a couple of months of hunting
experience with their parents, then are on their own. The "training period"
will only include techniques useful in the post-fledging season - nothing about
how to hunt in winter or in spring migration. The young birds use those
techniques until those prey are no longer as available, and then have to learn
to innovate, to hunt other kinds of prey. If you do a literature search on prey
types and hunting techniques for a species you might find a lot of diversity,
but if you can explore the diets of individual birds, you find them much more
specialized - each one has only figured out a small subset of the techniques
used by the species in aggregate. Here are three examples illustrating this
point.
1. Between 2011 and 2018 I spent a lot of time observing the Yaquina Head
Peregrines, and recorded over 100 individual prey items brought to the nest
area, and for most, knew which bird brought it in (total of 4 adult Peregrines
over that period). Each bird had ;particular prey that it brought in more
frequently. For example, in 2015 the original female brought in multiple downy
Western Gull chicks. Really easy to catch, but by unusual techniques for a
Peregrine - land on the ground, walk over and grab. The other three adults
apparently ignored this food source. In 2018, the second male brought in
multiple juv. Starlings that seemed to be right at the point of fledging. I
watched him hunting them by cruising in close along the concrete of the Yaquina
Bay bridge, trying to surprise birds by coming around corners and to the
entrances of crevices at speed and trying to grab whatever was too slow to get
out of the way. The other three birds did not bring in these particular prey,
although they did sometimes bring in adult Starlings. He apparently did not
figure this out until his third season there. This same bird hunted shorebirds
over the ocean a lot during the peak of shorebird migration around the
beginning of May. Multiple species were coming by in numbers, but most of his
captures were Short-billed Dowitchers. I think he had learned a technique that
was more effective on them than on the other species.
2. From the mid 1950s to the mid 1990s Dr. Bill Robertson, a good friend of
mine in south Florida visited the Bald Eagle nests in Florida B ay (Everglades
National Park) to check production of fledglings. By the end of that period
there were about 20 active nests each year. He also kept notes on remains of
food items under the nest. These birds were feeding from pretty much the same
smorgasbord, but the items differed varied wildly from nest to nest. Some had
mostly fish bones. A few were littered with the remains of small herons. One
nest, year after year had large collections of the shells of the small Mangrove
Terrapins (subspecies of Diamondback Terrapin).
3. Straying from raptors, but I think indicative of the same learning
processes, in 1974 I spent 2 months studying gulls on Destruction Island, up on
the Olympic Peninsula. Lots of the nests had regurgitated remains of food items
around it, and like the eagle nests, these showed a lot of individual
specialization. many were littered with the plates of Gooseneck Barnacles. One
had numerous small Razor Clam shells, so that bird must have learfned how to
hunt (dig?) clams on the mainland beach to the east. Others had mainly fish
bones, etc.
Wayne
From: "Larry McQueen" <larmcqueen@xxxxxxx>
To: roygerig@xxxxxxxxx
Cc: "obol" <obol@xxxxxxxxxxxxx>
Sent: Friday, December 13, 2019 9:58:54 PM
Subject: [obol] Re: Cooper's Hawk Behavior
Roy,
We know that accipiters have a great variety of hunting skills, and need them.
I suspect that many catching techniques are learned in the process of trial and
error. I also suspect that your bird once found a wounded or dead bird in the
underneath part of a vehicle, or chased a bird that took to the chassis. I’m
always amazed at bird behavior that looks like intelligence.
Larry
On Dec 13, 2019, at 5:42 PM, Roy Gerig <roygerig@xxxxxxxxx> wrote:
I got in my car this morning and then saw an adult COOPER"S HAWK in front of
me, across the narrow street where two guys park their high off the ground
pickups in the daytime
It watched and then flew down under one of those pickups, and walked around
underneath it for a minute or more, looking up into the wheel wells and on
the ground. Then it flew back up to a perch behind the pickup from me and
watched some more, then down underneath for the same routine...over and over
about 4 times before it finally flew over my head toward somewhere else in
the neighborhood
I have not seen this behavior before
Roy Gerig, Salem OR
