Abstracts: Lower Predation Risk for Migratory Birds at High Latitudes

L. McKinnon, P. A. Smith, E. Nol, J. L. Martin, F. I. Doyle, K. F. Abraham, H. G. Gilchrist, R. I. G. Morrison, and J. Bêty (15 January 2010) Science 327 (5963), 326. [DOI: 10.1126/science.1183010]

Quantifying the costs and benefits of migration distance is critical to understanding the evolution of long-distance migration. In migratory birds, life history theory predicts that the potential survival costs of migrating longer distances should be balanced by benefits to lifetime reproductive success, yet quantification of these reproductive benefits in a controlled manner along a large geographical gradient is challenging. We measured a controlled effect of predation risk along a 3350-kilometer south-north gradient in the Arctic and found that nest predation risk declined more than twofold along the latitudinal gradient. These results provide evidence that birds migrating farther north may acquire reproductive benefits in the form of lower nest predation risk.

There's a long standing debate on why birds migrate north to the arctic for the summer. This paper gives evidence that birds are migrating further to avoid predators. I suspect they're partially wrong, in that the initial (primitive) cause was more tired to taking advantage to seasonally available resources. Part of the lower predation risk is due to dilution effects (this is my suspicion), something the initial birds would not have enjoyed - dillution only works if there's many of you, not one or two.