On Mon, 21 Mar 1994 Ted Becker <tbecker at isumataq.eskimo.com> writes:
>
>I have heard from two different sources that the Snowy Owls that winter in
>the Puget Sound region are essentially dead birds. Having come this far
>south they have too far to go to get back to their summer habitat it time.
>
>This makes absolutely no sense to me. I can understand that they may not
>get back in time to breed but what would cause their death? Do they not feed
>enroute? Is there some other factor? Is there real evidence of this
>mortality or is it speculation? Is not mating fatal? I know that human
>males try to convince human females that not mating is harmfull, is it true
>of Snowy Owls?

I would like to know the sources of this--to me--ridiculous statement. Why
aren't such statements made about any other bird that winters here? The
"too far to migrate" hypothesis is no more sensible than the "have to mate
to live" hypothesis. Most of the ones that are here, adults or immatures,
leave some time in March, which is plenty of time to get back to their
breeding grounds. If all these immatures weren't going to breed, I might
suspect they would stay here in their first summer as many seabirds do. Or
if doomed to die, again they would hang around here until they did so.

There is plenty of evidence of Snowy Owl mortality on their
wintering ground, but I think this is because they are big and white and,
when found dead, the carcass is often turned in or at least reported to
some agency. Far, far more Red-tailed Hawks and Great Horned Owls are
picked up on roadsides and turned in to rehabilitators and museums. Birds
die all the time!

The usual hypothesis, that Snowy Owl flights come in years of
resource depletion (lemmings at low stage of population cycle) on the
normal wintering grounds, has been little documented. An alternative
hypothesis should be considered--that young Snowy Owls come down here in
large numbers after particularly successful breeding years, when there are
a lot of young birds. This would fit with the demography and dispersal of
many animals. It would seem to me that if lemmings crashed, then there
wouldn't be many young Snowies, the age stage that we see in large numbers
during invasion years.

Much more info needed, as far as I am concerned. Two relevant
papers (unfortunately I haven't looked at either one):

Kerlinger, P., and M. R. Lein. 1986. Differences in winter range
among age-sex classes of Snowy Owls (Nyctea scandiaca) in North America.
Ornis Scand. 17: 1-7.

Kerlinger, P., M. R. Lein, and B. J. Sevick. 1985. Distribution and
population fluctuations of wintering Snowy Owls (Nyctea scandiaca) in North
America. Can. J. Zool. 63: 1829-1834.

Note to Ted: I never thought of using that line!