Winter duration. The duration of winter hibernation is a critical component to understanding the metabolic demands of many bat species as insect resources typically disappear from the landscape during the coldest portions of the year. Despite this, relatively little information is available for the duration of this period and to-date no continuous estimation exists for North American bats. Therefore we estimated the winter hibernation period based on Myotis lucifugus as it is one of the most abundant and best studied bats in North America with a distribution spanning across the majority of the temperate zone (below the Arctic Circle and above the Tropic of Cancer). Records on bats immergence and emergence from hibernacula or duration of hibernation were collected from the literature, acoustic surveys, and from personal communications with local bat research groups (Hranac et al. accepted). The duration of hibernation was extracted from each location and a generalized linear model was used to correlate the number of days bats spend in winter hibernation with several abiotic variables. The top model selected by Akaike information criterion included terms for latitude, elevation, and the number of days of frost per year. Results were then projected back across the study extent to create a continuous estimation of the hibernation period (i.e., duration of winter) across the entirety of temperate North America (Hranac et al. accepted). All relevant code and products can be obtained from http://gitub.com/cReedHranac/wintor.