Stability and change through time in the dialects of a Neotropical songbird, the Rufous-collared Sparrow

Abstract

Behavioural characters that are learned can show temporal variation resulting from changes introduced in new generations during the learning process. The song of the Rufous-collared Sparrow (Zonotrichia capensis) shows significant geographical variation associated with habitat, delimiting song dialects. To study the temporal stability or change in dialects of Rufous-collared Sparrows at a microgeographical scale, we compared recordings made at Reserva El Destino, in north-eastern coastal Buenos Aires Province, Argentina, during 1987 and 2000 with recordings made during 2010 and 2011. We found that the geographical boundaries of the dialects remained stable over the period of 24 years. As we did not detect gross changes in the habitat of the study area over that period, we conclude that habitat is an important factor in maintaining geographical boundaries of dialects. Within the dialects, variation in some variables detected between 1987 and 2000 persisted to 2010-11 whereas other variables showed reversal over that period. These findings are consistent with the hypothesis that some changes in song were the result of neutral variation, whereby changes resulting from random factors, such as copying error, could have been maintained or introduced across generations. Our results show that comparing more than two points in time is fundamental to a better understanding of temporal variation of song and its possible causes.