Geographic Song Discrimination in Relation to Dispersal Distances in Song Sparrows

Abstract

Whether geographic variation in signals actually affects communication between individuals depends on whether discriminable differences in signals occur over distances that individuals move in their lifetimes. We measure the ability of song sparrows (Melospiza melodia) to discriminate foreign from local songs using foreign songs recorded at a series of increasing distances and compare the results with previous measurements of dispersal distances. We test discrimination in males using playback of songs on territories and measuring approach and in females using playback to estradiol-treated captives and measuring courtship display. Females fail to discriminate against foreign songs recorded at 18 km but do discriminate against foreign songs recorded at 34, 68, 135, and 540 km. Males fail to discriminate against foreign songs recorded at 18, 34, 68, 135, and 270 km but do discriminate against foreign songs from 540 km. Females are more discriminating, but even they do not discriminate at a distance three times the root-mean-square dispersal distance, as estimated from mtDNA variation. We suggest that female preference for local songs benefits females not because it allows them to reject foreign males but because accurate production of local song serves as a test of song-learning ability.

Song Function and the Evolution of Female Preferences: Why Birds Sing, Why Brains Matter

“…77,78 Equally problematic is the fact that, in species with gradual geographic variation, typical dispersal distances may make it unlikely that a female would ever hear a song outside the range that she accepts as equally attractive to local song. 72 Thus, the genetic adaptation hypothesis does not appear to be a general explanation for the evolution of female preferences for local song.…”

“…In most species, however, variation is more gradual with differences only apparent over broad geographic ranges. 72 In either case, females generally discriminate against songs recorded from foreign populations and prefer songs sung by males from their own local population. 73 The differences between songs from two geographic locales can be subtle 74 and it is unclear how producing songs typical of one locale can be more costly than producing songs typical of another.…”

“…Indeed, the common preference of females for local versus foreign songs may reflect the perception that they are less well learned. 72,114 The "developmental stress hypothesis" thus accounts for the widespread preferences both for more complex songs and for more local-sounding songs, with signal reliability being maintained by developmental costs in each case.…”

Territorial dynamics of Mexican Ant‐thrushes Formicarius moniliger revealed by individual recognition of their songs

“…Bird song parameters can vary substantially between geographically or environmentally distinct populations (e.g. Searcy et al. 2002, Leger & Mountjoy 2003, Kirschel et al.…”

Voice variance may signify ongoing divergence among black-legged kittiwake populations

“…Errors in social learning may accumulate and cause divergences between populations (Chilton & Lein, 1996; Irwin, 2000; Ellers & Slabbekoorn, 2003). Song learning is thus thought to generate geographic song variations, or dialects (Chilton & Lein, 1996; Searcy et al. , 2002), that have been proposed to result from divergent cultural selection or drift (Danchin et al.…”