The Savannah Sparrow is widespread and abundant in open habitats throughout North America although, like other grassland sparrows, it is often overlooked because of its secretive habits. During the breeding season its persistent buzzy song can be heard in agricultural fields, meadows, marshes, coastal grasslands, and tundra. Insects and other arthropods are its main prey in summer; in winter and on migration its diet shifts to small seeds found on the ground. Most populations are migratory, although salt marsh populations breeding in the southwest are mainly resident. As in many passerines, annual mortality of adults is about 50%. Adults tend to reoccupy the same breeding site, and in island populations birds commonly return to their natal site. Such strong philopatry has resulted in reproductive isolation and substantial geographic variation; 17 subspecies are currently recognized, including the Ipswich Sparrow, which breeds on Sable Island, Nova Scotia.
This species was named by Alexander Wilson for the town of Savannah, GA, where the type specimen was collected. Although the species is sexually monomorphic in plumage, males are generally about 5% larger in body size than females. Polygyny is routine in many populations, especially in the Canadian Maritime provinces.
Savannah Sparrows have been used as model organisms for the study of avian migratory orientation, with major contributions by Able and co-workers ( Able and Able 1990a ; Able 1991 ; Able and Able 1996 ). Several features of the biology of Savannah Sparrows make it attractive for comparative studies of ecology and evolution, including the species' broad geographic distribution, occurrence in a variety of habitats, high breeding densities, natal philopatry on islands, and evolutionary divergence of populations. Work by Dixon ( Dixon 1972 ) and Bédard and colleagues ( Bedard and Lapointe 1984a , Bedard and Lapointe 1984b , c) elucidated the basic ecology of Savannah Sparrows. Long-term studies of a population on Kent Island, New Brunswick and the application of molecular techniques have added to our general understanding of avian mating systems, behavior and evolution ( Wheelwright and Schultz 1994 ; Freeman-Gallant 1998 ; Wheelwright and Mauck 1998 ; Freeman-Gallant et al. 2003 ; Wheelwright et al. 2003 ).