Discrimination of song types and variants in song sparrows

Abstract

Male song sparrows,Melospiza melodia, sing highly variable songs. Traditionally, researchers have partitioned this variability by assigning songs to discrete categories termed ‘song types’, but researchers also have recognized that songs classified as the same song type are themselves variable. Territorial playbacks were used in a habituation/recovery design to investigate whether song sparrows perceive songs classified as separate song types to be more distinct from one another than songs classified as variants of the same song type. Cluster analysis was used to classify playback songs as song types or variants. Playbacks consisted of focal songs repeated for 1h, followed by a switch to 6min of either (1) a second variant of the focal song type from the same source male or (2) a second song type of the same source male. Twelve sets of playback tapes were used in a total of 96 trials. Subjects showed habituation in the response measure (distance to the speaker) during playback of the focal songs. Response recovered for between-song type switches, with mean distance to the speaker decreasing significantly between the last 3min pre-switch and the first 3min post-switch, and between the last 6min pre-switch and the 6min post-switch. For within-type switches, recovery was significant when comparing only the last and first 3min. Recovery was significantly greater for between-type switches than for within-type switches on both measures. These results suggest that in the perception of male song sparrows, different song types are more distinct than are different variants of a single type.