Plump songbirds more likely to survive migration over Gulf of Mexico.

A kilometer above Fort Morgan, Alabama, small migratory birds face a critical decision. Ahead lies a thousand kilometers of open water, the Gulf of Mexico, and a 22- to 24-hour flight without rest or food. On the other side, if they make it, they'll continue the journey to their South American winter habitat. For some, the journey will end in the waters of the Gulf.With many migratory birds in decline, ornithologists are keen to identify choke points along their routes. Large geographic barriers like the Gulf are likely suspects, but survival rates across these barriers are difficult to estimate. A new study published in Proceedings of the Royal Society B provides the first survival estimates for small migratory birds crossing the Gulf, and the factors that explain whether or not they survive the crossing.

We know a lot of birds die going across the Gulf because we see birds floating up on shore and in the stomach contents of sharks. We just don't know how many and how risky it is to go across the Gulf, says Mike Ward, lead author of the study, an associate professor in the Department of Natural Resources and Environmental Sciences at U of I, and avian ecologist at the Illinois Natural History Survey. We figured out that survival depends on a combination of how fat they are the fatter the better and how much wind they have at their back.