求翻译：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.是什么意思？

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