Impact of hydroelectric operations on the physiology of songbirds during fall migration

Habitat quality in riparian zones used by Neotropical migrants, important for migration success, will vary with changes in water level, an important management consideration for operation of hydroelectric facilities. I conducted a three-year study monitoring physiological condition of Fall migrants in relation to variation in water levels in four passerine species in Revelstoke, BC. Birds were blood sampled during migration and I measured plasma metabolites (triglyceride, glycerol, & β-hydroxybutyrate) and corticosterone (CORT) as indicators of fattening rate and environmental stress, respectively. Migrants had low baseline CORT and showed a robust stress response following capture, contradicting the Migration-Modulation Hypothesis. Estimated fattening rate (triglyceride) increased with time of day and date, reflecting diurnal and seasonal variation in fattening, and among species. However, fattening rate did not vary among-years despite marked annual variation in water levels. Plasma glycerol and β-hydroxybutyrate varied among years, but this was not consistently associated with high or low water levels.