Hi, tweeters.

Looking at the Sullivans' photos of Snowy Owls was a real treat. Did
you notice the little "horns" (ear tufts, head tufts) on some of
them? I still remember reading a magazine article many years ago when
the writer "discovered" and photographed those, supposedly for the
first time. As most of the field guides still have the old name
Nyctea scandiaca, you might be interested to know that the scientific
name is now Bubo scandiacus. Genetic data showed the close
relationship of the Snowy to the Great Horned and other large
"horned" owls of the genus Bubo.

I just looked in the Birds of North America Snowy Owl account by
David Parmelee (1992, one of the first ones published) and found some
material germane to recent discussions of the species. I'm hoping the
BNA lawyers won't get after me for disseminating this much of one of
the species accounts. Sorry, I don't know if you can get to the
reference links unless you have an online account.

Dennis Paulson
1724 NE 98 St.
Seattle, WA 98115
206-528-1382


TIMING AND ROUTES OF MIGRATION


The classic explanation of the species? irruptions implied that the
owl?s principal prey, lemmings, crashed along a broad tundra front
following a four-year peak, forcing the owls to wander in search of
prey. The fact that many Snowy Owls appear in s. Canada usually one
winter in four suggests that these irruptions are linked to the
lemming cycle, although admittedly the flights sometimes occur in two
successive winters, the second involving smaller numbers ( Fig. 3;
Godfrey 1986).

Recent observations on wintering Snowy Owls challenge the implication
of the classic hypothesis that a coordinated lemming-owl cycle is
geographically synchronous continent-wide. Although these owls show
unpredictable periodic irruptions in eastern and western North
America, a large majority appear to be regular migrants over much of
their winter range, notably in a central zone including the northern
Great Plains where they are especially abundant (Figs. 1, 3;
Kerlinger et al. 1985). Lacking hard evidence that lemmings fluctuate
synchronously over vast areas (Maher 1970), Kerlinger and associates
believed that the microtines occupied a mosaic of tundra patches
varying in size. Owl dispersion even in the favored winter midlands
is patchy, and the abundance of owls within patches may vary markedly
between seasons. Dispersion is thus thought to be linked to local
availability of their primary prey (Kerlinger and Lein 1988b).

Looking at the geographic dispersion of lemming abundance and Snowy
Owl breeding during any given year yields a mosaic. Peak numbers of
varying lemmings (Dicrostonyx groenlandicus) at high latitudes in
North America appear to be far less than peak numbers recorded at
lower latitudes where both the varying lemming and brown lemming
(Lemmus trimucronatus) occur in the same areas, or in those areas
where extraordinary numbers of only brown lemmings occur at times
(Parmelee 1972). Also, lemming fluctuations appear to be less regular
at the higher latitudes where owl clutches average smaller, judging
by a long-term study on Bathurst Island at 76?N in the Canadian
Arctic. Compounding the problem of synchronizing owl breeding with
lemming peaks is the fact that at least a few owls may breed during
periods when lemmings are only moderately abundant. Nevertheless, the
crux of the phenomenon is a mobile breeding population of owls that
move nomadically, breeding where and when their prey is abundant.

Not so easily explained are the large, geographically synchronous
winter irruptions that are observed in eastern and western North
America ( Fig. 3). Breeding areas for the birds involved in these
irruptions must necessarily be on the order of millions of hectares,
far greater than can be attributed to lemming mosaics (Kerlinger et
al. 1985). Other factors, possibly weather, i.e., the relationship
between snowfall and temperature conditions on the breeding grounds,
could be important. Herein lies a crucial, little known area in the
species? makeup that merits additional research.


MORTALITY AND DISEASE


Many Snowy Owls that move southward from arctic regions are
mistakenly assumed to die from starvation. Although this may prove to
be the case during irruptive migrations of young in western and
eastern sections of North America, there is no evidence that this is
so in the N. Great Plains. In Alberta, 45% of the specimens examined
had moderate to heavy fat deposits, and traumatic injuries were the
major cause of mortality (Kerlinger and Lein 1988a). Causes of death
or injury were collisions with unknown objects (46.5%), automobiles
(14.1%), utility lines (4.2%) and airplanes (1.4%); also gunshot
wounds (12.7%), electrocution (5.6%), fishing tackle (1.4%). Only
14.1% was believed due to starvation. Even as far south as Kansas, a
Snowy Owl fed on rodents at a lumberyard for nearly a month before
being accidentally electrocuted (Parmelee 1972). Gross (1947)
inferred that individuals seen far from land at sea never live to
return, but this is a moot question, difficult to resolve.


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