MEMPHIS, TN (WMC) - Geese winding their way south in a v-shaped flock is the classic picture of migration, the annual, large-scale movement of birds between their breeding (summer) homes and their non-breeding (winter) homes.
According to the website, allaboutbirds.org, of the more than 650 species of North American breeding birds, more than half are migratory.
Migration is described as a periodic, large-scale movement of populations of animals.
But why do birds move from location to another? The main reason is to move from areas of low or decreasing resources to areas of high or increasing resources. The two primary resources being sought are food and nesting locations.
Birds that nest in the northern hemisphere tend to migrate northward in the spring to take advantage of the increase in insect populations, budding plants and an abundance of nesting locations.
As the season changes to winter, the insect population and other food sources drop, so the birds move south again. Escaping the cold is one motivating factor, but many bird species, including hummingbirds, can withstand freezing temperatures, just as long as the food supply stays adequate.
While the migration initiating migratory behavior varies and are not always completely understood, scientists believe it can be triggered by a combination of changes in day length, lower temperatures, changes in food supply, and genetic predisposition.