An excerpt from Minnesota Birding, newsletter of the
Minnesota Ornithologist's Union, Nov/Dec 2004, p.13.
"Owls and
Voles -- Andy Jones
"As winter approaches, Minnesota's
birders begin hoping that the coming winter will be "a good one," with the
spectacular boreal and arctic species of owls moving south in large
numbers.... "Mammal and bird researchers in Europe have cooperated...
discovering that the voles that owls so often eat experience a cyclic
pattern of population fluctuation... "Surprisingly, such a pattern has
not been documented for North America... "Marianne Cheveau and three
collaborators from the University of Quebec - Montreal carried out a study
to search for correlations between mammal and owl populations in North
America.... They used information on Boreal, Northern Hawk and Great Gray
Owl distribution in winter ...This was complemented with data from ten
years of data from a small mammal population study throughout Quebec...they
found that the three species of owls tend to fluctuate
together... "...The years 1992, 1996, and 2000 all recorded low counts for
Red-backed Voles, demonstrating a four year cycle... All three winters
following these years were big invasion yeas for all three owls, especially
Boreals. "...the Boreal Owl ...is typically in more forested situations in
winter, where Red-backed Voles are most numerous. Northern Hawk Owls
are found in a larger array of habitats, and typically, include more birds
in their diet... Great Gray Owls are typically in more open habitats where
other mammal species dominate... "If the authors of this study are
correct, then the winter of 2005 should be and excellent one."
Harry
Krueger, IBLE List Owner
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