Albatrossity2
Posts: 2780
Joined: Mar. 2007
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| Quote (dhogaza @ Aug. 12 2011,22:15) | Well, it's been a cold and wet spring throughout much of their range, so there's a good chance they won't make it, and we'll see one of those natural variability events regarding survival rates of a variety of raptors (and other species) that are migratory.
Banding migrating hawks in the Great Basin for many fall seasons (a couple of decades), one thing I've noticed is that in some cold spring years, some species (accipiters, esp) pass by in lesser numbers, but those that are caught and banded have laid down heavier body fat than normal. While in large first-year migration years, the kids have often been skinny. Seems that things might balance out a bit in terms of migration survival and initial health on the wintering range.
This is just anecdotal, I'd love for some grad student to dive into this data to see if there's really anything to it ... |
I dunno if it was a cold wet spring in that part of Colorado, but it was certainly a droughty summer! I've never seen it so dry there; even Medano Creek, which runs along the eastern edge of the Great Sand Dunes, was completely dry most of the summer.
There still seemed to be lots of jackrabbits and cottontails, however, probably because much of that valley is irrigated alfalfa and potato cropland. So I suspect that a Swainson's Hawk could still make a decent living there.
That's an interesting observation about the amount of body fat related to low or high-recruitment years and spring weather. If it was mostly in the accipiters, maybe they just got extra fat picking off the dickie-birds who didn't have as much cover as usual. 
Did the buteos show the same pattern?
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Flesh of the sky, child of the sky, the mind
Has been obligated from the beginning
To create an ordered universe
As the only possible proof of its own inheritance.
- Pattiann Rogers
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