Why Do Birds Migrate?
About 350 of the approximately 650 birds in America migrate.
Birds do not migrate like humans - to chase the weather. Birds, including hummingbirds, can survive the cold quite well - if there is enough food.
Some birds, Cardinals for example, are able to find adequate food in the northern part of the northern hemisphere year round and therefore, do not migrate.
Birds migrate to seek food and nesting habitat. Insects, seeds, worms, etc. and favorable nesting habitat are in abundance in the northern part of the Northern Hemisphere in the summer months.
When birds migrate south for the winter, they do so to varying extents. Some birds migrate short distances to seek lower elevations. Some birds migrate just a few states away. Some birds migrate long distances to another continent.
It is not fully understood why birds living in tropical locations in the winter migrate north in the summer. One theory is that evolution favored species that did so, as the abundance of food, and longer days, allowed for better reproduction (more offspring) relative to the birds that remained in the tropics.
Migration is triggered by genetics, day length, temperature changes, and food supply.
Migration navigation is an astounding phenomenon that is poorly understood. How do birds that have never migrated know how to do so their first time, for example? Scientist think that birds use the earth's magnetic field, star patterns, the sun's position, scents, and visual landmarks for navigation.
Hummingbirds have been known to return to the same backyard feeder in the spring after two 1000-mile journeys.
Hummingbird in nest at Wall Lake.
Many birds migrate at night because night brings fewer predators, calmer wind currents, lower temperatures, and food is typically eaten during the day at important migration staging areas, like Wall Lake.
A recent discovery is the presence of very small iron spheres in the hair follicles in the ears of birds. These are called are called magnetoreceptors. Scientists speculate that this may aid in the use of the earth's magnetic field during migration.
The bird that migrates the longest distance is the Arctic Tern, flying a total of 44,000 miles per year between the Arctic and Antarctic.
Sometimes we can't even find the car keys!