Biology Reference
In-Depth Information
selves. And if they survive the dangers of the night, come morning, they have to negoti-
ate whatever habitat they find themselves in.
Citiescanbetreacherous.Anestimated500milliontoonebillionbirdsarekilledeach
year in the United States in collisions with windows. Many of these deaths take place
at lighted high-rise windows at nighttime, and many take place in the morning against
plate glass windows and doors at ground level, when birds find themselves in a heavily
urbanized area where the only vegetation is inside hotel lobbies and solariums. Habit-
at degradation, especially along coasts and shorelines, can make obtaining food difficult
for migrants right when they need it most. As a wildlife rehabilitator, I cared for several
loons, grebes, and rails (shy little marsh birds) that had crashed onto sparkling wet pave-
ment where a wetland existed the previous year.
One researcher found that apparent mortality rates of Black-throated Blue Warblers
were at least 15 times higher during migration than during the breeding and winter res-
ident periods; more than 85 percent of apparent annual mortality of this species occurred
during migration!
You can see a map of where any wintering species were reported in mid-February in
the United States and Canada during any winter since 1999 on the Great Backyard Bird
Count map; the website is www.birdcount.org.
What Birds Do in the Winter
Q Do birds nest again once they reach their wintering grounds?
A No. Northern birds spend winter eating food in the tropics and, sometimes, molting
intonewfeathers.Raisingyoungtakestremendousamountsofenergy,andfewmigratory
species can afford to do that for longer than a fairly brief period of time in their annual
cycle.
Canada Geese were introduced into Great Britain as early as the 1600s. Four centuries
later, the geese on the British Isles are still non-migratory. Canada Geese were intro-
duced into Sweden during the first half of the 1900s. These geese have become migrat-
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