Birds respond more strongly to locally common versus locally rare songs: a playback experiment with Savannah sparrows.

Animals' learned vocalizations often show high levels of intraspecific variation, and different variants may play different roles in attracting mates and settling territorial disputes. In any animal population with variable vocalizations, certain acoustic variants may be common and others rare. The responses of animals to local versus nonlocal sounds have been well characterized in prior investigations, but few investigations have explored the reactions of animals to songs that are present at different frequencies of occurrence within a population. Using an experimental approach to investigate a breeding population of Savannah sparrows, Passerculus sandwichensis , we tested the responses of territorial male songbirds to playback of locally common songs, locally rare songs and heterospecific songs. Male sparrows showed strong responses to conspecific song but weak responses to heterospecific song. Males showed their strongest responses to locally common songs and weaker responses to locally rare songs. Birds did not appear to discriminate between playback songs based on whether they were of the same song type as their own. We suggest that male Savannah sparrows perceive locally rare songs as weaker threats than locally common songs, similar to birds' reactions to foreign dialects. This could be due to low familiarity with locally rare songs, reduced female preference for locally rare songs, decreased success with territory defence for males singing locally rare songs or other perceived differences between locally rare and locally common songs. Overall, our results suggest that different song types elicit different responses from territorial songbirds, even songs that are found within the same population with different frequencies of occurrence. • Many animals show small-scale geographical variation in vocalizations. • Responses to locally common or locally rare vocalizations are seldom explored. • We used playback to test birds' responses to locally common and locally rare songs. • Savannah sparrows responded more strongly to locally common songs. • We suggest locally common songs are perceived as a stronger threat. [ABSTRACT FROM AUTHOR]