Meeting Abstract
Hummingbirds can use torpor to reduce metabolic rate overnight as part of a strategy to manage daily energy balance or to maximize energy storage during certain life stages. However, the rules that govern torpor use are unclear. While torpor may be used only during times when energy stores fall below a critical level, an ‘emergency only’ strategy may be abandoned to facilitate fat conservation prior to and during migration. We tracked body composition and torpor use in male ruby-throated hummingbirds (Archilochus colubris) throughout the breeding season and the beginning of the fall migration period using quantitative magnetic resonance, respirometry, and thermal imaging. During the summer, birds that entered torpor did so at very low estimated fat stores (~5% of body mass). Interestingly, torpor use occurred repeatedly during the migratory period in birds that had accumulated high body fat stores (>20%). Overall, our preliminary results suggest that in the breeding season, hummingbirds use torpor only when their energy reserves are especially low. However, torpor use with high fat stores in the migratory season suggests that some individuals are able to use torpor to facilitate storage of fat needed to fuel their migratory journey. Ongoing analyses aim to explore individual variation and to elucidate the mechanistic link between torpor use, and seasonal changes in body condition.
