Individual variation in migratory path and behavior among Eastern Lark Sparrows

Abstract Two general migration strategies prevail among temperate-breeding migratory songbirds of North America. Most “Eastern” birds migrate relatively directly from breeding to wintering grounds immediately after molting, whereas a substantial proportion of “Western” species depart breeding grounds early, and molt during extended migratory stopovers before reaching wintering areas. The Lark Sparrow is one of a few Western Neotropical migrants with a breeding range that extends into regions dominated by Eastern species. We sought to determine whether Eastern Lark Sparrows migrated in a manner consistent with Western conspecifics or follow typical Eastern songbird migratory patterns. To do so, we tracked individual Eastern Lark Sparrows equipped with geolocators between their breeding grounds in Ohio and their unknown wintering locations. Data from three Ohio Lark Sparrows revealed 1) individual variation in the duration and directness of autumn migrations, 2) autumn departures that consistently preceded molt, 3) wintering grounds in the central highlands of Mexico, and 4) brief and direct spring migrations. These observations suggest that eastern populations of prevailingly Western migrants, such as Lark Sparrows, may be behaviorally constrained to depart breeding grounds before molt, but may facultatively adjust migration en route.