Use and Possible Functions of The Primary and Sustained Songs of Male Grasshopper Sparrows

Abstract

Ascertaining the functions bird song requires information about when and where a song or, for males with multisong repertoires, songs are used. Because the need for and type of communication with mates and conspecifics changes with breeding stage and social context, detailed observations may reveal differential use of song or of different song types. Our objective was to examine the use, and determine the possible functions, of the two song types (primary and sustained) in the repertoire of male grasshopper sparrows (Ammodramus savannarum) by observing males throughout the breeding season and in different behavioral contexts in Madison County, Kentucky. For primary songs, rates varied among breeding stages and were highest before pairing, suggesting that primary song plays a role in mate attraction. However, male Grasshopper Sparrows continued to use primary songs after pairing, and likely functions include territory defense. The use of sustained songs also varied among breeding stages, with none uttered before pairing and rates highest during nest building and incubation. Male grasshopper sparrows also uttered more sustained songs when being observed (with one of us in their territories) then when not (neighboring males). These results suggest that sustained songs may serve to alert females to the presence of potential predators while simultaneously distracting such predators. Songs with such functions appear to be uncommon and have been reported in few other species.