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Discussion of other Raptor species; their anatomy, biology, ecology, etc.
Topic Started: Sep 16 2007, 11:04 AM (18,134 Views)
ostrich2
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I was sent some very interesting information on counts of the local (and migrating) raptor populations in Toronto by someone on another site - this may be interesting to look through - a lot more species than I would have imagined! It might be worth it for me to try to go out to some of these locations - perhaps it will give some insight on what my other unusual sightings might have been.

This blog has some summaries as well as some pictures:

Rosetta McClain Gardens Raptor Watch



Greater Toronto Raptor Watch
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Raptorman
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ostrich2
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At first glance the idea of the Coopers drowning prey seemed a bit implausible to me, just from considering the question "what would be the survival advantage". I would have thought that drowning prey wouldn't obviously be any better a way of dispatching the prey than what the hawk already has at its disposal (i.e. talons and beak), and actually trying to drown the prey you'd also think would involve some danger of (a) being immersed in the water with risk of drowning itself, or (B) losing grip on the prey and it then being lost if it sinks and is not retrievable.

However, this reference describes a Cooper's apparently "drowning" in a captive situation:

Cooper's Hawk 'drowning' its prey

This article also describes an observation of a Cooper's doing something similar:

Unusual behaviour of a Cooper's Hawk
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ostrich2
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Hmm - on the topic of the Cooper's hawk, this picture is very reminiscent of the bird I mentioned seeing chasing songbirds outside my building, at least in terms of the coloration and plumage patterns.

Posted Image

I wonder if it could possibly have been a Cooper's - the sparrows would make more sense as a prey for a Cooper's than a RT, and the bird was definitely smaller than a full sized RT.
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Raptorman
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Bea
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Raptorman,Oct 20 2007
07:59 PM
...
On the Cooper's Hawk claims the killing is often done with the talons by constriction or puncturing. Many kills by many raptors is actually achieved during the process of consumption not by grabbing or biting. So the prey is alive while consumption begins.
...

That is exactly what we observed when the Coopers Hawk landed in our yard with the starling as prey. It started "plucking" it while the starling was still alive.

Thank you Bill, for all your info and answers to my questions! :D
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Bea
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ostrich2,Oct 20 2007
08:53 PM
At first glance the idea of the Coopers drowning prey seemed a bit implausible to me,  just from considering the question "what would be the survival advantage".  I would have thought that drowning prey wouldn't obviously be any better a way of dispatching the prey than what the hawk already has at its disposal (i.e. talons and beak), and actually trying to drown the prey you'd also think would involve some danger of (a) being immersed in the water with risk of drowning itself,  or (B) losing grip on the prey and it then being lost if it sinks and is not retrievable. 
....

Ostrich, those are exactly my thoughts when I first read about "drowning prey". I would agree that there would be a certain amount of danger to the hawk involved in drowning it's prey, so why would it not simply kill it in the usual manner (talons and/or beak).
Thanks also for the links to those articles you found. The accounts of those reports date back a long time, and Bill has a hard time finding confirmation on drownings, so that leads me to believe that this drowning the prey-thing would definetly not be "usual" behaviour, but maybe just the "exceptions to the rule" perhaps?

Bill, thanks so much for trying to find more info on this subject!
This sorta turned into my assignment for you, huh? :lol:
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ostrich2
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Raptorman,Oct 20 2007
10:59 PM
Many kills by many raptors is actually achieved during the process of consumption not by grabbing or biting. So the prey is alive while consumption begins.

Do you mean that the initial capture (presumably by the talons) isn't always immediately fatal and thus the prey sometimes doesn't expire until consumption is underway, or that the raptor starting to consume the prey is actually necessary to dispatch the prey in some cases?

For most raptors, you would tend to think that the talons deliver such injury on impact that although it might not cause instant death, the prey is essentially already expiring almost immediately. So it becomes in a way a kind of "if a person jumps off a building and someone shoots them while they're passing by their window what killed them" type of question.

The biggest prey delivery I have seen is the delivery of the live rabbit to the Saanich eagle nest last year - and that was very much the impression. The rabbit was clearly still alive when the adult brought it into the nest and began the consumption process for the eaglets, but it was just barely so and probably would have quickly expired in any case.

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ostrich2
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Bea,Oct 21 2007
10:58 AM
Ostrich, those are exactly my thoughts when I first read about "drowning prey". I would agree that there would be a certain amount of danger to the hawk involved in drowning it's prey, so why would it not simply kill it in the usual manner (talons and/or beak).
Thanks also for the links to those articles you found. The accounts of those reports date back a long time, and Bill has a hard time finding confirmation on drownings, so that leads me to believe that this drowning the prey-thing would definetly not be "usual" behaviour, but maybe just the "exceptions to the rule" perhaps?

Yes, this is quite possible. It might be a rare behaviour that does happen, or it's not beyond the realm of possibility that it is a characteristic of a specific population that's not true of the species as a whole. From the sounds of it the behaviour has probably only been seen anecdotally (perhaps even just from those old observations). It might well be a behaviour that no one's taken the time to study scientifically in detail so even if it has validity there might not be a lot of hard data on it.

Although it's hard to imagine why the hawk would want to drown the prey, that doesn't mean there isn't a real benefit to the hawk that isn't obvious. Often behaviours in nature can be based on very subtle advantages and tradeoffs to the animal.
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Bea
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ostrich2,Oct 21 2007
09:03 PM
Raptorman,Oct 20 2007
10:59 PM
Many kills by many raptors is actually achieved during the process of consumption not by grabbing or biting. So the prey is alive while consumption begins.

Do you mean that the initial capture (presumably by the talons) isn't always immediately fatal and thus the prey sometimes doesn't expire until consumption is underway, or that the raptor starting to consume the prey is actually necessary to dispatch the prey in some cases?
...

I think that's exactly it. On page 3 are the pictures of the hawk with the starling. If you look closely, you can see the hawks feet standing on each wing of the starling. There was no pressure whatsoever to the body or head of the prey, and, the Hawk positioned himself that way purposly! He started plucking chunks of feathers from the starlings chest, and would have "eaten the prey alive", had he not gotten disturbed by a noise and flew off with his prey "still very much alive".

:)
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Raptorman
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ostrich2
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For those who have been following the Brisbane peregrine cam, Naturegal posted a screenshot today that shows the chick is quickly starting to develop pin feathers:

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ostrich2
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Another interesting sighting today - I spotted what was definitely a raptor flying over a grassy hill - as I was just getting on a ramp to the highway I had a chance to stop by the side of road and watch it for a bit.

Although it was definitely very hawk-like, what caught my attention was that it was flying in a rather kestrel-like manner - the wind was quite strong and it was hovering over the ground, facing into the wind and just flapping gently every few seconds to keep itself just about stationary. That didn't seem to be a very hawk-like thing for it to do, but then I found some references that state that RT's will do this:

http://en.wikipedia.org/wiki/Red-tailed_Hawk

Quote:
 
In flight, this hawk soars with wings in a slight dihedral, flapping as little as possible to conserve their needed energy. Active flight is slow and ponderous with deep wing beats. It sometimes hovers on beating wings and sometimes "kites", or remains stationary above the ground by soaring into the wind


One thing this bird seemed to have that I haven't yet found a specific description of for the RT is what looked to be small dark patches right near the ends on the underside of the wings.
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Raptorman
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ostrich2
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By the ends of the wings I meant near the tips of the wings, not along the trailing edge. Since RTs can have those, I'd say it was probably a RT. If it wasn't for the kiting behaviour I saw, I would have just assumed it was a RT since they are so often around the area, and they're the ones you most commonly see. It certainly looked like a RT in all other respects.
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