November 21, 2009
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December 06, 2009
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December 19, 2009
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I posted a question to MassBird a week ago about a pair of Cooper’s Hawk that are wintering in the neighborhood and wanted to share some of the information that was most generously sent my way. MassBird is an invaluable resource and so are the fine folks that participate on this list sharing their knowledge so freely. Thank you very much to all that replied: The questions: What would a pair of Cooper’s Hawks be doing together at this time of year? Aren’t they solitary except in breeding season? The short answer is that I most likely have a family unit consisting of an adult male, adult female and a hatch year roosting in the pines and utilizing the yard as a food resource. Images of 2 of the hawks (the female joined the fray this week, along with a Red-shouldered and a hatch year Sharp-shinned) as well as the text below can be seen at: http://www.nebirdsplus.com/CoopersHawk.htm The answers surprised me. From Paul Roberts: Hi Phil, I have not had time to do further research, but I did pass your email along to Larry Fisher, who has been following nesting accipiters in Connecticut for 25+ years and knows as much about accipiter nesting as anyone I know. He sent me the following, which is consonant with some of what I know about Red-tailed Hawk behavior with fledged young (Wintering Redtails also can roost communally, with the communal “roosters” including some of their young, and conceivably, offspring from previous years – all untagged birds.) I know that with immature birds and subadults seeking mates, some Bald Eagle pairs have tolerated “au pairs” assumed to be female, and you have the subadult third-party at the Mississippi Kite nest in New Hampshire, and Peregrines courting with younger females until their successful female from the previous year returns and competes for the male. When I first read your post I was thinking that it could well be a young female (not offspring of the male), seeking an older male as liaison and possible provider and mate.
Hope this is of help. From Larry Fischer via Paul Roberts: “The very short answer is that female accipiters solicit food from males throughout the year. This is apparently regardless of any blood or pair bonded relationship. Here’s the long answer: At the heart of the question seems to be the belief that adult raptors drive their young from the territory. This is in fact is a false assumption. There does come a time when the adults stop presenting prey to their young and force them to fend for themselves. At that point the young can get very physically aggressive towards the adults begging for and even trying to take food away from their parents. The adults may be forced to defend themselves by going on the offense and driving the young away from themselves, not out of the territory. I think it is this weaning process that for such a long time has been interpreted as “being driven from the territory.” After this process has played out, I have seen young raptors that I banded in the nest peacefully hunting within the adults’ territory. Speaking specifically about Cooper’s hawks, I’ve often seen birds in immature plumage living peacefully within an active breeding territory, even as close as the edge of the nest woods. If one thinks about it this makes sense as a healthy breeding population has new recruits readily available in the event that one of the adults dies. A C Bent in his LIFE HISTORIES OF NORTH AMERICAN BIRDS OF PREY: Part I, The Cooper’s Hawk, talks about the rapid replacement of adults shot and collected from the nest including adult females being replaced by adult females. Breeding adult male Cooper’s hawks, in any given year, establish a flyway in and out of their nest woods. Most prey deliveries to a sitting female will be made using this flyway. One May, positioned along a flyway with a good view in both directions, I heard the shrill food begging cries of a young Cooper’s hawk. I turned to watch an adult male carrying prey being closely followed by a female in immature plumage begging to be fed by the male. Both birds flew by me below tree top level and flew into the nest woods where a female in adult plumage was sitting on her clutch of eggs. I couldn’t see what happened but I expected to hear a lot of loud “cacking” and to see the young female make a hasty retreat but instead I saw and heard nothing. I suspect that there was the usual soft “cacking” that occurs during a normal food transfer between the breeding pair but I was too far away to hear that. The question in my mind was: is this one of the young from the previous year or was it a young female unrelated in any way? Without a patagial tag it’s impossible to tell. I don’t think it matters; healthy populations have ready replacements. One December, doing some follow up research in a white pine grove where Cooper’s hawks had nested successfully the previous spring, I heard some “cacking.” I looked up to watch a female in adult plumage chasing a male in adult plumage; the male was carrying prey. Was this the female from the previous spring? Again, without a patagial tag there was no way for me to know. Food begging involves a series of actions and calls and may include individual variations but in general, female accipiters in immature plumage have a shrill cry that to me can sound like a child crying or whining in the distance. Females in adult plumage also use this shrill cry but also add adult “cacks” and “hics.” Adult and immature females also will sit on a branch fluff up their feathers, crouch, whine, and sometimes shiver; or they may chase the male “playfully” or aggressively. Sometimes this chasing takes place below the canopy and sometimes it can be high in the sky. Of the half dozen banding returns on Cooper’s hawks banded in the nest and retrapped or found dead it appears that immature females disperse much shorter distances from their natal territories than immature males. That is to say that they stay further north. On the other hand, adult males appear to stay on their breeding territories year round. (Keeping in mind that the sample size from banding returns is statistically very small) It is interesting to speculate that young females may begin to establish bonds with adult males during the winter. It is also interesting to speculate that perhaps even if or when the adult female returns in the spring, the adult males may continue to maintain a relationship (feeding them but not breeding) with these young females. Again I would suggest reading AC Bent’s chapter on the Cooper’s hawk paying particular attention to how fast collected females are replaced by new females.” From Tom Carrolan: The 11/21 images are of a CH of the year. I can't guess the sex as the tail is not hanging down for a proportional look. If this bird and the adult male are your two then this is family unit activity where the young are still around the nest/territory [I didn't get if these birds have been there all summer]. (they have) So where's the adult female? Have you seen her around? Nice adult male Coop with the square tail and even a central indentation [used to be that was a Sharpie tell, but we know better now] Birds of North America is good stable stuff, but as I written about before, it primarily utilizes info published in peer-reviewed journals and monographs, so that restricts it from being current in terms of observations by non-academic/government folks. I've also written a bit about the number of raptor species pairs that I've observed in migration as well on wintering grounds. The old idea that raptors are solitary (as in big mammalian predators) is a myth for most raptor species at the high point in their life histories. I just posted a DNA study this week on my blog about eagle fidelity and, for my part, showed non-local pairs of Bald Eagles in February (2 pairs within a mile of each other... likely together thru the year). I blogged about a Coop v. Crow encounter in early November in the Syracuse NY area that ended in a pair of adult Cooper's Hawks perched tight together beneath the crows. November is getting late for migrating birds, but if that's the case then here they are together. If local birds, then here they are together on territory. In this case, I cruise this road often and they are not around in Winter to my knowledge. Here's a link, cutting to the ending images, showing the male-female-together shots. Again, whatever the situation, here they are together way, way after the breeding season: From David Ely: Hi Phil, While I can't specifically speak to whether or not specific family groups will stay together over the winter, I can say that I've seen communal roosting of Cooper's hawks in the midwest and Colorado in suitable habitat. I've seen groups of 3-8 Cooper's together in the winter in windbreaks, usually with a strong Russian olive component mixed with coniferous trees. They are often with long-eared owls in these areas. This is most likely resource exploitation and not necessarily representative of pair or family bonds. On the one hand, I have often seen cooperative hunting behavior with Cooper's in my yard in Broomfield, CO. I've seen up to two at a time in my yard and if I recall one of the birds is usually a younger bird with an adult. One bird typically "hides" in cover (which is a pinon pine in my yard) and the other bird drives feeder birds into the cover where the other Cooper's hawk is waiting. This has occurred principally during the migration seasons and I think does represent a family bond with birds traveling together. I have seen this in the spring before hatch-year birds are around and therefore it would indicate a bond that was maintained over the winter. David Ely |
All photos © Phil Brown 2009
