Many birds migrate thousands of miles every year, but while some use tried-and-true migration routes, others go with the flow... the wind flow that is.
Every year, millions of North American songbirds migrate thousands of miles to from North America to Central and South America and vice versa. For years, scientists could only speculate how the bird were making these journeys, but a new study reveals how they do it. They rely on wind patterns.
According to the report, "The role of atmospheric conditions in the seasonal dynamics of North American migration flyways,” published in the Journal of Biogeography in April 2014, "Avian migration strategies balance the costs and benefits of annual movements between breeding and wintering grounds. If similar constraints affect a large numbers of species, geographical concentrations of migration routes, or migration flyways, may result. Here we provide the first population-level empirical evaluation of the structure and seasonal dynamics of migration flyways for North American terrestrial birds and their association with atmospheric conditions.”
Much of what is known about bird migration comes from shorebirds, which follow a narrow path in their routes known as "flyways.” Songbirds don’t have to rely on the same habitats as the shorebirds do, but scientists had no real way to study their flyways because they migrated at night. By using data submitted to the Cornell Lab’s eBird project from 2004 to 2011, scientists got their chance to figure out the songbirds traveled.
© Laura Erickson
Birds such as this clay-colored sparrow use the central flyway identified in the study "The role of atmospheric conditions in the seasonal dynamics of North American migration flyways."
According to Cornell University Media Relations Office press release, "researchers analyzed thousands of sightings to develop, for each of 93 species, an aggregate picture of where a species is during spring and fall migration. Although they weren't tracking individual birds, collectively the sightings gave them an indication of how the species were migrating. They then used computer models to sort species with similar movement patterns into groups. They also compared migration routes with seasonal patterns of prevailing winds at night.”
By sorting the birds with similar migration patterns together, scientists came up with three main groups: 31 species in a western group, 17 in a central group; 45 species in an eastern group. Birds like the black-throated gray warbler, a western species, use the western flyway; the clay-colored sparrow, which breeds in the Great Plains, used the central flyway; the American redstart used the eastern flyway. Scientists also found that central and eastern groups have overlapping routes. The data showed that many birds migrate in similar elliptical, clockwise routes.
They also found that birds took advantage of strong tailwinds in the spring and weaker headwinds in the fall on their routes. The research gives scientists and researchers to form conservation plans for birds based on the different migratory routes.
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