Finding Their Way: Understanding Whooping Crane Migration
I've always been amazed by how birds find their way along lengthy migratory routes each autumn and spring. Turns out I'm not the only one. Scientists have also been intrigued by the phenomenon for quite some time and have devoted much research to expanding their understanding of bird migration.
There are several explanations researchers have come up with that describe how birds find and follow their migration paths.
One explanation is that birds learn the route from fellow members of their flock—older birds teach younger birds to follow the correct migratory route. A second explanation is that birds find their way on their own. Individual birds teach themselves by trial and error how to navigate between breeding and wintering grounds. A third explanation is that birds are born with an innate knowledge of the route—they are genetically programmed to follow a certain path.
Of course, in nature things are rarely straightforward. One or more of these mechanisms may be at work for any given bird species. Different bird species might learn their migratory routes in different ways. So scientists often study individual species to find out more about how that particular species migrates.
Recently, a team of scientists led by Thomas Mueller from the University of Maryland analyzed 8 years of data on migratory whooping cranes. The whooping cranes Mueller and his colleagues studied belonged to the eastern migratory population, a group that migrates between its breeding grounds in Necedah National Wildlife Refuge (Wisconsin) and Chassahowitzka National Wildlife Refuge (Florida).
Since the birds were captive-bred, their genetic relatedness was well documented. Additionally, the birds were trained to follow ultralight aircraft on their first migration southwards. This meant all birds were initially trained to follow the same migration route. After that first ultralight-led training migrations, the birds migrated freely in groups with other older and more experienced birds. Thomas Mueller's team teased apart the effects of learned migration and genetic programming by evaluating several variables including the age of individual birds, the age of the oldest member of a migratory flock, the size of the flock, and the genetic relatedness of the birds in the flock. They found that in flocks in which the oldest individual was 8 years old, the flock deviated less (29 miles) from the ideal migration route than flocks whose oldest individual was only 1 year old (such flocks deviated about 47 miles from the ideal route).
These results indicated that for whooping cranes, older birds play an important role in teaching younger birds the best migratory path. It also shows that it takes time to learn the appropriate migration route and that birds learn this route over several years.
Cranes and their relatives (Gruiformes) are a group of birds that includes coots, rails, crakes, bustards and trumpeters. The group consists of about 199 species. The members of this group are collectively known as the Gruiformes. They are varied in their size and appearance, but generally have a short tail, long neck and rounded wings.
The cranes are the largest of the Gruiformes and among them is the tallest flying bird on the planet—the sarus crane which stands over 5 feet tall. Cranes have long legs and long necks and an impressive wingspan measuring between 6 and 7 feet. Most cranes are predominantly pale grey or white in color with accents of red and black feathers on their face. The black-crowned crane is the most ornate of all cranes with a tuft of golden bristle-plumes atop its head. There are 15 species of cranes worldwide.
Thomas Mueller et al. (2013). Social Learning of Migratory Performance Science, 341, 999-1002 : 10.1126/science.1237139