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BIRDING 101
LESSON 6: NATURE'S MARVELOUS CLOCK


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.

(Photo by Marcus Martin)

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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