Birds Migrate in Search of Food

by Kevin Strauss

While it still seems like summer, some bird species are already getting ready for fall migration. I have noticed small flocks of sparrows foraging for seeds in my back yard and fattening up for their trip.

While some people assume that birds migrate to avoid our cold winters, that isn’t exactly true. Many bird species that live up here during the summer could survive our winters, if they could find enough food. A bird’s downy feathers are the best natural insulators in the world. Even small birds like black-capped chickadees survive our winters by eating oily seeds to put on fat and then clustering together and shivering through our sub-zero nights. The real reason that birds migrate is their search for food. Ruby-throated hummingbirds feed on flowers and as many of our northwoods flowers are going to seed, these hovering birds are preparing to move south to the lands of still-blooming flowers.

Insect-eaters like the nighthawks are also preparing to leave in search of more mosquitoes, moths and other flying insects. Nighthawks are those birds that appear at dusk over town, swooping on white-banded wings and “peenting” as they scoop up insects with their wide mouths.

While scientists used to think that birds timed their migration based on the decreasing hours of daylight as fall approached, further research refutes this claim. In a recent study, migratory bird species were kept in cages in a room with no windows and given a constant twelve hours of light each day. Despite receiving constant levels of light, the birds began to exhibit “migratory restlessness” as winter approached. They began to perch on the south sides of their cages and become more active at night. Night is the time when most birds migrate. These studies suggest that it isn’t hours of sunlight that trigger migration. Birds must have some other year-long, possibly hormonal, “clock” that tells them when to migrate.

It also seems that birds don’t use landmarks or other guides to determine how far to travel. In a separate study, researchers captured migrating birds and trucked them down to their winter feeding grounds. But when researchers released the birds, the bird continued migrating south. They migrated, on average, the same distance that the trucks had carried them. This lead researches to conclude that birds migrate south until their “migratory restlessness” ends. This seems to be regulated by hours of flying, not the distance traveled. So once a bird has flown a certain number of hours, it settles down for the winter.
As we move through August, watch for birds that are gathering for the big trip south.