Almost 40 percent of bird species are migratory, with their own flight paths and patterns
How birds choose their flight paths during migration
April 17, 2018
Marking seasons with bird migration
Bird migration is a yearly spring and summer ritual. Remember all of those times you’ve looked into the sky and witnessed birds flying north to south? It’s especially true of geese, flying in that “v” formation. People have marveled about bird migrations for thousands of years. Some of the events have even made it into popular culture. For example, the swallows returning to Mission San Juan Capistrano, California forms a legend. The buzzards returning to Hinckley Reservation, a Metropark near Cleveland, hasn’t reached legend status yet, but it has become an event as well. There are many other examples around the world.
Birds know what to do
What makes the migrations even more amazing is that almost 40% of bird species are migratory birds. And each species has its own route, with departure and arrival dates, its own way to travel (making stops or flying as far as possible) and its own habits (flying solo or with a group).
“The birds are really accomplishing two separate but related tasks,” says John Brzorad, Ph.D., director of the Reese Institute for Conservation of Natural Resources at Lenoir-Rhyne University. “They have to orient and they have to navigate. Think of orientation as a compass and navigating as a map.”
Day-length, position of sun and temperature changes all trigger migration
So how do the birds do it? It appears that the length of daylight, or the changing ratio of daylight to darkness, as well as temperature, triggers the instinct to migrate. Once in the air, it’s been shown that birds use their knowledge of landscapes to know which way to fly. Birds follow rivers, coastlines, and mountains on their route. Birds also use the location of the sun as well as the stars to navigate. Experiments letting birds fly in a planetarium and changing the stars’ positions confirm this.
Scientists also believe the earth's magnetic field may play a role. Some birds have a small zone of magnetite (magnetic material) at the base of their brain that could act as a small compass. “The amazing thing is that birds have an array of tools to use to cover vast distances,” says Brzorad. “And it seems to work every year.”
Frank Graff is a producer/reporter with UNC-TV, focusing on Sci Tech Now North Carolina, a weekly science series that airs Tuesdays on UNC-TV. In addition to producing these special segments, Frank will provide additional information related to his stories through this North Carolina Science Now Reporter's Blog!
Video: The Great Migration