I saw Ryan Brady's weekly report for the DNR Digest regarding some unusual
birds that are remaining in Wisconsin this winter. They include, among
others, hermit thrush, several species of sparrows, plus catbird, Baltimore
oriole, rose-breasted grosbeak and a few warblers. I wonder if these late
season records might fall into two categories or have different reasons for
remaining so late into winter.
Some birds, like hermit thrush, robins, white-throated sparrow, red-winged
blackbird and grackles are found during winter in small numbers in most
years. This might also be the case for yellow-rumped warblers that are
short-distance migrants. The relatively mild weather could allow a few more
of these to stay in Wisconsin this year.
However, long-distance migrants, such as orioles, grosbeak, indigo bunting,
Cape May warbler and catbird shouldn't be here and certainly aren't
expected to be winter residents. As the days become shorter this signals
birds to head south so they should be long gone before cold weather sets in
and most of their food supply disappears. There likely are individuals
that either don't get the signal or are not fit to undertake the migration
and would account for late season records. I would guess that there are a
few of these long-distance migrants that get left behind every year. I
would doubt that they would remain because they expect a mild winter since
they would have no idea what kind of weather we will have. When most birds
are preparing for fall migration there is no way of them predicting what
the weather trend might be several months out.
In a normal Wisconsin winter I would think that any long-distance or
neotropical migrant that gets left behind perishes fairly quickly and
doesn't remain that late into the year. It makes me wonder if the mild
winter is simply allowing these birds to survive longer into the season?
With so many people watching birds and also reporting their sightings we
might be documenting these occurrences more than in the past.
Bill Volkert
FdL Co.
Bill Volkert
Naturalist
www.billvolkert.com
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