POSTFLEDGING DISPERSAL, HABITAT IMPRINTING, AND PHILOPATRY IN A MONTANE, MIGRATORY SPARROW

Movements of White-crowned Sparrow Zonotrichia leucophrys oriantha fledglings in relation to their nest sites were measured for 37 broods on a large subalpine meadow, Tioga Pass Meadow (TPM). Broods were split between the parents upon fledging and the resulting family subunits appeared to move independently. Three weeks after fledging and about when young were becoming independent, family subunits were located a mean distance of 200 m from their nests. Additional data on movements of independent juveniles were obtained from a trapline on TPM in which we captured individuals originally banded in their nests either at TPM (locals) or at other sites (nonlocals) up to 5 km away from TPM but within the same watershed. Although some siblings traveled together at least until fall migration, considerable dissolution of families occurred at 35 to 40 days of age. At that same age, nonlocal juveniles began to appear in the TPM trapline. First captures of known age nonlocals of both sexes from within a 5 km radius of TPM peaked at age 50-55 days. The majority of nonlocals were probably more than 60 days of age upon arrival at TPM, however, and we assumed that they probably had also traveled more than 5 km from their natal sites. We hypothesize that young migratory birds may disperse in order to find favorable staging areas and/or to become acquainted with an array of local landmarks that could provide important information for their subsequent navigational and homing abilities. Selection of the next year's breeding site could also occur during post-fledging dispersal. If it occurs, the habitat imprinting or site selection process must differ somewhat between males and females. The more time juvenile males spent on TPM the more likely they were to return there as adults. Of those known to be on TPM for 30 days or more, the return rate was 28.6%. Philopatric tendencies were considerably less in females. About 10% of those trapped as juveniles returned later as adults regardless of the number of days they had spent on TPM as juveniles.