I'm thinking more about crows and owls. It's a substitute for actually knowing, so please chime in, Anne, or anyone else who knows better than I do what really goes on. I've been impressed by how much the Great Horned Owls in Renwick have withstood crows' harassment, and that impression flavored my earlier comment.
A big purpose of the harassment of owls by crows ought to be to drive the predators away so the owls will cease being a danger to the harassing crows. But it doesn't look to me like it would work very well. Great Horned Owls are low-light, quiet, fairly slow (I think), stealth hunters, and in the daytime they are not a danger to crows nor to anyone else.
A roosting owl might be convinced to move, but would it move far enough to shift its nighttime hunting area? Where would it not be in some crows' territory? At some point the owl has to stop being driven, and I have heard crows quit. Nesting owls, if they are to be successful, and obviously sometimes they are successful, must not be ousted by crows for several months, starting in early winter, when (I assume) crows are not defending territories nor clearing them of owls starting a nest. Last spring's crow nest can make a nice owl nest, which must be a disheartening discovery, to find owls living smack-dab in the middle of the territory when the crows return at the end of winter.
In autumn and winter crows may travel for miles to roost during the night when owls are hunting. By gathering thousands of crows out of outlying owls' hunting territories, crows might improve their individual odds, but I would think that any owl residing near the massive crow roost, or who came to visit, would have easy eating. Maybe the crows make a special effort to clear owls from the crow roosting neighborhood, but the roost is so obvious that I wonder how much good it would do.
In the crow nesting season, of course, the crow female and young are stuck and vulnerable. Again, the crows have a good reason to try to drive an owl away, but I would think that a Great Horned Owl can still travel a long distance to hunt, and a crow nest which I can see in a tree during the day is probably similarly obvious to the owl at night. The crow nesting season starts after the owls are well underway. Do crows choose not to nest near Great Horned Owls? I bet the owls' hunting ranges so large as to encompass several crow nests anyway.
I assume that the harassment of owls has some direct benefit in terms of predation reduction, but I doubt it's very large. I think either crows harass owls so much because that's one of the few things they can do to reduce predation when they can afford the time and energy, or else there are other benefits, such as getting to know what a Great Horned Owl looks like, or showing off for other crows, or crow family bonding, or being generally useful to the crow flock, or socializing, or getting exercise, or even having fun.
Crows' lot looks very frustrating - and dangerous - regarding Great Horned Owls. I sympathize with the crows, too, but also I find their situation more complex and hard to figure.
--Dave Nutter
Right--and come mid-April, some person might just pick up a partly eaten, headless, tagged female crow under her nest and think...it was her first nest--what a short life, only 5 years, her nestlings gone, too! She could have had 6 more years at least, or more.Boredom probably doesn't describe why the crows leave off (have seen them harrying owls for at least 6 hours)...nor a lack of memory for why they start over the next day. The crows aren't moving on...they are trying to move a dangerous thing out of their neighborhood, where their own kids need a chance at life.Yup--I took the bait. The story is all in your perspective, but I always find US interesting in siding with the one who has the kids at the time!Holding no grudges against owl-lovers,AnneOn Feb 16, 2013, at 2:05 PM, Mona Bearor wrote:I'll be thinking of your explaination when I visit the nest again, and I'll be watching for that owl to sigh and plan its nightly menu!Mona Bearor So. Glens Falls, NYOn 2/16/2013 12:21 PM, [email protected] wrote:I think this is the sort of crap that Great Horned Owls have to put up with, and they get used to it. I suspect that what you saw is probably the pattern. Every day some crow "discovers" the owl, still in the same place on its nest, and raises the alarm, just as it would for an owl roosting in a new spot every day. All the other crows join in for awhile, so the whole crow community is aware of its presence, and the younger crows learn, "We don't like these guys." When they're satisfied and bored with lack of reaction from the owl on the nest, they move on. The owl sighs, reminds itself to eat some of those bastards come nightfall, and continues incubating, brooding, or guarding its young.--Dave NutterYesterday morning I observed about 50 crows mobbing a Great Horned Owl on a nest. It made me wonder if the crows could make the owl abandon the nest with repeated harassment, or if they would just give up after a while. I had an appointment so I couldn't stick around too long, but did watch this behavior for over 20 minutes non-stop. The owl was still on the nest today.
Any thoughts on this?
Mona Bearor So. Glens Falls, NY--Cayugabirds-L List Info:Archives:Please submit your observations to eBird!--
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