Energetics and Migration in Songbirds: Two Case Studies Examining Energetic Condition and Migration at a Northern Stopover Location

Abstract

Migration is an energy-intensive behavior undertaken in both spring and fall by billions of songbirds to reach distant breeding and wintering grounds. Stopover habitats, particularly those located near ecological barriers that birds must cross, provide key locations where birds can stop and refuel during migration. A bird’s energetic condition affects its behavior at stopover locations; in spring, birds may accumulate energy reserves at locations en route to breeding grounds for tasks other than migration. This two-part study examined different aspects of the energetic condition of songbirds at a northern stopover location on the south shore of Lake Ontario. First, banding data for 12 Parulidae species were analyzed, and I found that arrival date, sex, and season explained some of the variation in the energetic condition of birds arriving at this location. My results suggest that there is possibly a reproductive advantage for spring migrants to arrive with energy reserves. Second, I found that energetic condition affects the orientation of White-throated Sparrows (Zonotrichia albicollis), mainly in the spring. However, like other studies of sparrows in captivity, I found bimodal orientation along the migratory axis, which makes it difficult to predict migratory orientation based on energetic condition. Both of these studies demonstrate that songbird behavior during migration is complex, variable, and worthy of further study.