At 05:33 PM 2/22/98 -0800, Michael Price wrote:
>

>>Barn Owls seem to lead a short life. In an 18-year study in Utah, it was
>>found that Barn Owls first bred at a little over one year of age, and on
>>average only got one year of breeding. Only 12 % of breeding birds still
>>have descendants after four generations. Harsh winters led to a low number
>>of second broods in the following year, and killed a lot of birds. Survival
>>rate until the first breeding is estimated at 30 %.

I've read the results of a study that indicate that in Utah, overwinter
survival depends very much on snow depth. I wonder if it was the same
researchers who did the above work?

Anyway, in winters where more than a certain depth of snow accumulated,
massive die-offs occurred. When only a relatively thin layer of snow
accumulated, overwinter survival was much higher. This was a study in
NE Utah. They get snow accumulation just about every, if not literally
every, year so the mortality stuff given us by Michael may not extrapolate
to areas with less accumulation in typical years. Apparently snow depth
beyond (I think it was 8) "y" inches led to the owls being unable to
locate or capture prey. Less than that, they could locate prey under
the snow.

These researchers seemed to think NE Utah was very marginal for barn
owls.

It would be interesting to see a study here in western Oregon, where snow
never accumulates for very long.


- Don Baccus, Portland OR <dhogaza at pacifier.com>
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