Familiarity, homogeneity, and discrimination of song dialects: Data and playback study stimuli

Male songbirds of many species sing local song dialects that are
restricted to defined geographical areas. In most tests of responses to
local versus foreign dialects, males respond more aggressively to songs
from their own dialect, presumably because local males represent more of a
threat to their success. We asked how hearing foreign songs during
development and territory establishment affects discrimination of the
local dialect in wild Savannah sparrows, Passerculus sandwichensis. After
foreign songs had been heard from loudspeakers in the study area in at
least two consecutive breeding seasons, males reduced the intensity of
their responses to the local version of population-specific buzz segment
of the song. Four years after the foreign songs were last broadcast on the
study area, males again responded more aggressively to the local version
of the buzz. As for the basis of these responses, we found no evidence
that birds discriminated among dialects by comparing them to their own
songs. However, auditory experience with a foreign song, whether during
song development (from speaker-simulated song tutors) or during the
current breeding season (from neighbours’ songs), reduced the intensity of
birds’ responses to the local buzz type. Both familiarity, in the form of
auditory experience with a song type, and homogeneity, when a song type is
sung by all or nearly all of the population, appear to contribute to
heightened aggressive responses to a local song dialect.