Ecological influences on vocal development in the white-crowned sparrow.

Gambel's white-crowned sparrow, Zonotrichia leucophrys gambelii, is a long-distance migrant that, in contrast to other subspecies of white-crowned sparrow, does not form vocal dialects. I studied the process of vocal development in the field and laboratory to determine how it differed from the process in three other subspecies previously studied. Four common song types existed in a random spatial pattern in my 2.6-km(2)study area. Of 106 males studied in 2 years, all arrived at the beginning of the breeding season singing their adult repertoire and no male changed his song during the season. In the laboratory, hand-reared males overproduced as much as other migratory subspecies of white-crowned sparrow. They learned their songs during the shortest sensitive phase of any white-crowned sparrow yet studied. In contrast to other subspecies that form vocal dialects, male gambelii chose their final adult song at random from their overproduced repertoire. I suggest the absence of vocal dialects in Gambel's sparrow results from the short, delayed breeding season on their sub-Arctic breeding grounds. The short breeding season has favoured a narrow sensitive phase in hatching-year birds, and prevents the extended vocal interactions among adults that lead to vocal dialects in populations breeding at temperate latitudes. Copyright 1999 The Association for the Study of Animal Behaviour.