About the Author
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Naturalist, wildlife photographer and writer Stan Tekiela is the
author of more than 175 field guides, nature books, children’s
books, wildlife audio CDs, puzzles and playing cards, presenting
many species of birds, mammals, reptiles, amphibians, trees,
wildflowers and cacti in the United States. With a Bachelor of
Science degree in Natural History from the University of
Minnesota and as an active professional naturalist for more than
25 years, Stan studies and photographs wildlife throughout the
United States and Canada. He has received various national and
regional awards for his books and photographs. Also a well-known
columnist and radio personality, his syndicated column appears in
more than 25 newspapers and his wildlife programs are broadcast
on a number of Midwest radio stations. Stan can be followed on
Facebook and Twitter. He can be contacted via
www.naturesmart.com.
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Excerpt. © Reprinted by permission. All rights reserved.
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FLIGHT BY DAY OR BY NIGHT
Many birds migrate during the day. Some of these daytime
migrators rely on rising columns of warm air, called thermals, to
help carry them upward. As the sun rises higher during the day,
it warms the land and creates thermals. Cranes, storks, hawks and
other large birds seek thermals and ride them like elevators to
the top. As the air rises higher, it cools and slows down. When
birds ascend to the top of a column, they glide off effortlessly
in the direction of travel and find another thermal to ride.
Swallows, swifts and other birds that eat flying insects migrate
during the day, feeding while they fly. Many other birds, such as
woodpeckers, jays, bluebirds, robins and blackbirds, make short
flights during their trips and stop to feed. Typically, it takes
these birds much longer to arrive at their destinations.
Daytime migrants usually start the day promptly at dawn and spend
their first couple of hours feeding. Migration gets underway
shortly afterward, with most birds taking off at around 10 a.m.
Many of these birds will feed again at the end of the day before
resting for the night.
However, the majority of small birds, known as the passerines,
migrate almost exclusively at night. Most of these birds start
migrating during twilight, about 30 minutes after sunset.
Passerines usually migrate by themselves, not in large flocks.
Other birds may be migrating at the same time and going in the
same direction, but these birds aren’t in an organized flight or
making a coordinated effort.
Modern radar and radio tracking devices have shown that the
numbers of birds migrating at night start to build slowly. It’s
not until around midnight that the numbers begin to peak. The
a of migrants in the air tapers when sunrise nears, with
most of the birds landing before daylight.
PERKS OF FLYING AT NIGHT
There are a number of good, sound reasons why birds would migrate
at night. The obvious reason is that they evolved into this
behavior. Because so many bird species today migrate at night,
scientists propose that in the past, the most successful birds
also migrated at night. They suggest that over time, the
descendants of the surviving nighttime migrators became the
dominant species.
Flying at night allows birds to feed and rest during the day.
Each morning the birds will land in a new place that they do not
know, making the task of finding food just that much harder. They
use the daytime hours to find enough food to fuel the coming
night’s activities.
The atmosphere at night is much more favorable for flight than it
is during the day. At night, the air has less turbulence, which
makes it attractive to slow-flying small birds. Typically,
nighttime airflows are more flat (laminar), providing better
support for birds in flight. Air temperatures are cooler as well,
reducing the stress of overheating and dehydration associated
with long, strenuous daytime flights. Moreover, birds don’t need
to stop as often to cool off, making it possible for them to fly
farther each night and finish their trips earlier.
In addition, there are fewer predators hunting for birds that
migrate at night. And equally important, navigation with the
stars is perhaps easier than using geography to plot the course
of the route during the day.
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