Vol. 44, No. 6
David M. Larson
Dark-eyed Junco. Photograph by A. Drauglis (CC BY-SA 2.0).
Many of New England’s favorite bird species are migratory, including wood warblers, shorebirds, waterfowl, and seabirds. These birds largely breed in the north in the summer and migrate to more temperate to tropical climes during the nonbreeding seasons. There are significant physiological advantages to avoiding the harsh winters of the Arctic or Boreal forests. And there are significant reproductive advantages to migrating to the Arctic or Boreal zones for breeding, including abundant food and space for raising young. The evolution of this migratory strategy in so many taxa gives proof to its utility. But with benefits come costs and migration is a perilous practice. Mortality rates are higher in migratory populations than in similar nonmigratory populations, especially during the difficult first year. Increased predation, collision, and disease are all obvious causes of mortality. In addition to these acute effects, other challenges include increased oxidative stress, immunological challenges, and weight fluctuations or even breakdown and reconstitution of muscle and organs.