Mike Sievering, Supervising Wildlife Biologist
During autumn, short days and cool nights trigger a phenomena that has occurred for thousands of years. During this time of year, large numbers of birds begin migration towards their wintering grounds.
Many species of birds travel thousands of miles in this semi-annual event. Species such as the blue-winged teal, which summers in northern Canada and Alaska, spend the winter months in South America. This same migration pattern occurs in the majority of waterfowl. Ducks and geese are well known for their migratory techniques, traveling thousands of miles over a variety of landscapes and large expanses of water.
How is it possible for birds, particularly waterfowl, to migrate or find their way year after year to the same wintering grounds? The answer is not a simple one; a multitude of factors come into play to make migration possible.
Migration seems to be triggered by a combination of shortening days and seasonal temperature changes. In addition to these environmental changes, physiological changes occur in the birds. These physiological changes cause migrants to literally gorge themselves in an attempt to build enough fat reserves for their upcoming flight. In other words, fat equals fuel for the impending journey.
Once migration is initiated, how do birds find their way? Since waterfowl migrate in flocks, the adults simply lead the way or teach the young the way to the wintering grounds. A variety of theories have suggested a multitude of ways migrating waterfowl find their way. The four most popular methods are visual orientation, sun compass, celestial navigation, and geomagnetism.
Visual orientation, or the utilization of geographic landmarks, such as rivers, coastlines and mountain ranges is a popular method used by birds that migrate in the daytime. This is especially important when it comes to finding precise breeding or wintering areas.
The use of a sun compass is a method that has been proven time and time again. It appears that many birds can use the position of the sun to provide information for correct migratory direction.
Celestial navigation is primarily used by waterfowl. Since most species of waterfowl migrate during the night, they utilize the position of the stars to guide them on their long journey south.
Geomagnetism, or the use of the earth’s magnetic field for orientation, is another method that is utilized by migratory species.
Each method has drawbacks if used individually, but if used simultaneously, many species of birds successfully migrate thousands of miles each year using these techniques.