Meeting Abstract
Facultative migration is characterized by unpredictable, highly variable patterns of movement that vary in both direction and timing across years. For many facultative migrant species it is hypothesized that a reduction in food availability triggers migratory behavior in an attempt to locate more favorable habitat. Corticosterone may mediate this transition, as increased corticosterone levels are associated with increased locomotor and foraging activity in both obligate and facultative migrants. Pine siskins (Spinus pinus) are a nomadic, irruptive migratory finch whose primary food source (conifer seeds) is also characterized by a high degree of spatial and temporal variability in abundance. We examined the effect of reduced food availability on migratory behavior and physiology and whether changes in behavior and/or physiology were associated with increased corticosterone levels. We measured locomotor activity, body mass and fat deposition, and circulating corticosterone levels for birds that experienced a food restriction and birds with ad libitum access to food. Food-restricted birds had higher daytime, but lower nighttime, activity levels compared to control birds. Corticosterone levels were also higher in food-restricted birds relative to control birds but returned to baseline levels within two weeks of returning to ad lib food. These results suggest that a reduction in food availability increases locomotor activity, which is associated with an increase in corticosterone; these results are similar to those from another facultative migrant (red crossbills). Pine siskins can migrate diurnally and nocturnally, however, reduced food availability may result in activity shifting to daylight hours, as this would facilitate assessment of new habitat to determine resource abundance.
