Meeting Abstract
Organisms that inhabit regions with high environmental variability must cope with sudden shifts in climatic conditions to survive and reproduce. In areas with steep elevation gradients, temporary movement from an area of high elevation to low elevation, facultative altitudinal migration (FAM), is a useful adaptation that promotes survival but may come at a cost to reproduction through the loss of territory or abandonment of a nest. White-crowned sparrows (Zonotrichia leucophrys oriantha) that reside in Tioga Pass Meadow, CA (elevation 3,030 m) are migratory and typically arrive in early May from their wintering grounds in Mexico. Snow cover is usually 100% and late spring snow storms are not uncommon. Furthermore, lower elevation refugia in the Mono Basin (~2,000 m elevation) are readily available. As such, this is a model population to investigate environmental and physiological variables that influence FAM behavior. Furthermore, this population has a relatively high rate of return allowing for an estimation of year to year survival. Here we review research on this single population spanning several decades and synthesize recent findings in a framework that includes environmental variables, physiological variables, and return rate in regard to FAM behavior. The physiological variables include glucose mobilization, glucocorticoid physiology and body condition. For FAM events that include corticosterone binding globulin measurements we will also discuss the difference between free corticosterone (CORT), total CORT, and bound CORT in reference to the Free Hormone Hypothesis, the Total Hormone Hypothesis and the Reservoir Hypothesis.
