Meeting Abstract
Severe climatic events during the breeding season can induce behavioral responses that favor individual survival at the potential cost of within-season reproductive success. For example, white-crowned sparrows (WCSP) breeding at high elevation can experience heavy snowfall during both pre-breeding territory establishment and during nest incubation. In the Tioga Pass, CA population (~3,000 m), lower elevation refugia in the Mono Basin (~2,000 m) is readily available and facultative altitudinal migration (FAM) during storms is documented. Predictors of FAM occurrence and duration include body condition, fat score, glucocorticoid physiology, and glucose mobilization capacity. Here we document the occurrence of FAM during the early-breeding season over three years (2015-2017) using radio-transmitters and an automated receiving unit. In 2015-2016, which coincided with a period of drought, there were zero cases of FAM among WCSP outfitted with radio transmitters. In 2017 a significant snowfall event occurred on June 11-12, and all eight WCSP with radio transmitters exhibited FAM.The length of time WCSPs were absent from their breeding territory ranged widely from 2,025-6,340 min (34-106 hours). We obtained individual glucocorticoid and glucose mobilization profiles as well as several measures of body condition during pre-storm stress trials. All WCSPs exhibited stress-induced plasma glucocorticoid and blood glucose levels. Interestingly, the rate of glucocorticoid increase was a significant negative predictor of FAM duration; which is consistent with other studies of glucocorticoid mobilization and territoriality in passerines.
