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It's February. The wind is blowing, snow
is covering my driveway and I'm looking out
into this raw, gray world in the grip of
winter. Then I hear it! The resonant love
call of the Great Horned Owl booms across
Burch Creek (which is part of my extended
backyard). Have you ever wondered why Great
Horned Owls begin their nesting season in
February but the American Goldfinch waits
for June? Why Black-headed Grosbeaks head
south in September but Black-capped Chickadees
continue eating sunflower seeds from the
feeder all year long? Or, why flowers seem
to know whether their kind bloom in early
spring or late summer? It's that marvel of
nature known as the biological clock.
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(Photo by Marcus Martin)
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We humans try to ignore our natural biorhythms.
We tend to be controlled by alarm clocks,
TV schedules, and calendars. We have substituted
precision and predictability for natural
cycles. We have designated artificial points
as significant milestones for life's activities.
This makes communication between individuals
easier but also creates some problems. The
biological clocks of our wild neighbors are
definitely Y2K ready!
Many factors contribute to the natural rhythms
of our wild birds. However, daylight seems
to dominate the daily cycles (diurnal, nocturnal,
and crepuscular) and day length seems to
play a major role in migration and breeding
cycles. Diurnal species are those most active
in daylight; nocturnal species are active
at night. Species, like the Common Nighthawk,
which are active at twilight are said to
be crepuscular. Body temperatures tend to
follow the activity cycles. Body temperature
of birds active in the day are higher in
the day and species active at night have
a higher body temperature at night. Light
seems to be the main factor controlling these
daily rhythms. Artificially changing the
light cycle will change the body temperature
cycle and also change the feeding or breeding
cycle in some species.
Adaptations, over a long period of time,
have lead to the timing of these cycles and
the different timing among different species.
For example, the Great Horned Owl needs to
capture small rodents (mice) to successfully
feed its young. Small rodents are easier
to catch in the early spring when vegetation
cover is at a minimum and rodents are more
active and visible as they try to obtain
food from a limited supply. On the other
hand, American Goldfinches require an abundant
supply of insects for early brood care, and
then a good supply of seeds as the young
become independent of their parents. These
conditions are optimal during late summer
and early fall.
Extensive research on biorhythms and the
timing of everything from feeding to singing
to breeding to molting to migrating has produced
many answers, but there is more to do. The
Wasatch Audubon Society is initiating a project
to add to this data base. We are asking everyone
to keep a record of when the first migrants
reach the Ogden area each spring. So, read
more details in the "Chickadee"
and start keeping a record of the first Black-headed
Grosbeak, or Bullock's Oriole, or Blue-gray
Gnatcatcher that shows up in your yard each
spring.
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