Ed, I'm a firm believer in crow farming also. It has long seemed obvious to me that they are searching for bird nests as they move around the neighborhood. We have an active Bushtit nest in the yard that I suspect will be hit at some point, as all previous nests that we have found in our yard have been (ditto with robins, as far as I know). Of course the crows can't possibly know the size of the young in a Bushtit nest, so if they wait until the appropriate time, it proves that crows can judge time! Perhaps they look up the incubation/fledging periods on Birds of North America Online. Or can they judge the frequency of feedings or the size of prey brought to the young?

Interestingly, female cowbirds must have the same search strategy for bird nests, but in their case they do their brood parasite thing just after the nest owner lays its first egg. I should add that cowbirds have declined in Seattle in recent years.

It's no wonder that hole nesters generally do fairly well in our urban/suburban settings, as they are impervious to predation by crows and most other predators. But of course robins and Bushtits and a few other cup-nesters are still common in Seattle, so many of their nests must escape predation.

I agree that your hypothesis about nighthawks is reasonable, but as Purple Martins and Chimney Swifts have both declined substantially in the East along with nighthawks, and they are not subject to crow predation, there may be other factors at play, in particular the decline of large insects. It's also possible that something in the Amazon basin, where these three species winter, could also be contributing to the problem.

Dennis

On May 10, 2012, at 12:39 PM, Ed Newbold wrote:

> Hi all,
>
> It's been a dismal year so far at Butyl Creek (the recirculating creek in our backyard here on residential Beacon Hill, Seattle) but we did have a Nashville Warbler in yesterday evening and 2 Orange-crowns just bathed with a Wilson's Warbler a minute ago.
>
> This morning I saw an incident that further convinces me that Crows "farm" bird nests. I heard the local Robin family getting excited and calling urgently for backup, but I was still slow to look up from the computer. When I did I was surprised to see a Crow in a horizontal dive in my direction, evoking the image of a Cooper's Hawk, and headed straight for the Holly tree where the Robins have a nest. Without ever slowing down, the Crow pulled a full-sized baby out of the nest and was gone.
>
> What's interesting about this is that about three weeks or a month ago the Robins got terribly upset and called me out. At that time I was armed with a Super-soaker and I chased a Crow away. That Crow's behavior was not really attacking, it was perched in the Holly tree peering around, and it's behavior was totally consistent with a reconnaissance mission. It left the area.
>
> Obviously nothing here proves anything, but I see these events as consistent with the notion that Crows are locating nests, waiting for the nestlings to reach max. weight while still immobile, and then making their move. It would also explain generally that when I've witnessed Crow predation, it always seems to be of a full-size nestling.
>
> Well, I don't expect a single person in tweeter-land to agree with me, but maybe at least I can get some sympathy for two suddenly unemployed Robins.
>
> And two more thoughts: The Holly-tree the Robins nested in is dense, but getting less so as it ages. Are young non-native Holly trees the best (only?) hope for tree-nesting species in the urban zone? Birds clearly need armored vegetation for any hope of safety from Crows, and native vegetation doesn't seem to offer much. I would think twice before removing Holly from yards in the urban zone for environmental reasons.
>
> The other is, I've long believed that Crows are the main reason for the loss of our formerly abundant Nighthawks. If Crows can find nests in Holly trees, how could they ever miss one on an open rooftop?
>
>
> Just wondering,
>
> Ed Newbold ednewbold1 at yahoo.com
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-----
Dennis Paulson
1724 NE 98 St.
Seattle, WA 98115
206-528-1382
dennispaulson at comcast.net



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