Researchers from the University of Delaware have discovered that migratory birds prefer to travel during the night. Should they still be flying by daybreak, the birds would immediately turn back and head for the nearest shore instead of continuing their journey. Using weather radar to examine the behavior of birds crossing the Great Lakes, the researchers were able to discover this unique behavioral pattern.

Jeff Buler, an assistant Professor of Wildlife Ecology of the University of Delaware, and Kevin Archibald, an undergraduate researcher who specializes in analyzing biological data, authored the study appeared in The Auk: Ornithological Advances, which is published by the American Ornithological Society. Using the U.S.'s powerful network of weather surveillance radar stations on birds heading north across the Great Lakes during their spring migration, Archibald and Buler noted that birds that were flying over the water increase their elevation and often turn back as dawn started to break. This behavior led to a buildup of birds in near-shore stopover habitats. Birds that took off from the southern shores of the Great Lakes on subsequent spring evenings was 48 percent higher than on the northern shores.

As birds migrate south during the fall season, they tend to increase their altitude at dawn to determine how much farther they have to travel. Should they judge the distance to be too far, they will attempt to try again the following night. This results in higher concentrations of migratory birds along the nearby shores, resulting in more pile-ups on the north side of the lakes rather than the south.

"Our study justifies the high value of shoreline habitats for conservation of migratory bird populations in the Great Lakes region," said Buler. "It also emphasizes that the extent of stopover use in shoreline habitats is context-dependent. We hope professionals charged with managing stopover habitats recognize that shoreline areas can receive high migrant use by virtue of the proximity to a lake and how many migrants are aloft at dawn from day to day, rather than [just] by the presence of abundant food sources in these habitats."