Many small endotherms use torpor to reduce metabolic rate and manage daily energy balance. However, the physiological "rules" that govern torpor use are unclear. We tracked torpor use and body composition in ruby-throated hummingbirds (Archilochus colubris), a long-distance migrant, throughout the summer using respirometry and quantitative magnetic resonance. During the mid-summer, birds entered torpor at consistently low fat stores (~5% of body mass), and torpor duration was negatively related to evening fat load. Remarkably, this energy-emergency strategy was abandoned in the late summer when birds accumulated fat for migration. Migrating birds were more likely to enter torpor on nights when they had higher fat stores, and fat gain was positively correlated with the amount of torpor used. These findings demonstrate the versatility of torpor throughout the annual cycle and suggest a fundamental change in physiological feedback between adiposity and torpor during migration. Moreover, this study highlights the underappreciated importance of facultative heterothermy in migratory ecology.

Funding provided by: Natural Sciences and Engineering Research Council of Canada Discovery GrantCrossref Funder Registry ID: http://dx.doi.org/10.13039/501100000038Award Number: 06129-2015 RGPINFunding provided by: Human Frontier Science ProgramCrossref Funder Registry ID: http://dx.doi.org/10.13039/100004412Award Number: RGP0062/2016Funding provided by: Natural Sciences and Engineering Research Council of Canada Discovery GrantCrossref Funder Registry ID: http://dx.doi.org/10.13039/501100000038Award Number: 05245-2015 RGPINFunding provided by: Canada Foundation for Innovation, Ontario Research Fund*Crossref Funder Registry ID: Award Number:

This metadata describes the data and code used in "Reversal of the adipostat control of torpor during migration in hummingbirds". The objectives of the study were to clarify the rules of torpor use in hummingbirds, by investigating the relationship between body composition and torpor use in. We used respirometry to calculate rates of energy expenditure, and quantitative magnetic resonance (QMR) to measure body composition of captive ruby-throated hummingbirds (Archilochus colubris). The included R scripts and datasets are used to process, analyze, and plot data described in this study.