Methods for assessing artificial thermal refuges: Spatiotemporal analysis more informative than averages

Abstract

1Thermal refuges are widely used by animals of all taxonomic groups and are critical to survival in severe weather. 2Human activities are reducing the availability of natural refuges; consequently, artificial refuges are used as conservation management tools, particularly for bats. 3Published box evaluations are generally incomplete, omitting thermal physiology and relevant thermal properties. 4Here, we compare methods for evaluating the potential utility of bat box designs for bats and present a graphical spatiotemporal method that provides more complete information. 5For illustration, we compare the original to three modified versions of the “rocket box” style bat box. 6Box internal temperatures and generalized thermal physiology models are combined in two suitability indices appropriate to the mother, and to pups. 7Results revealed that daily and seasonal averages of these indices obscured important processes and showed insignificant differences among bat box design modifications. 8In contrast, graphical analysis highlighted the presence and spatiotemporal structure of significant differences among boxes, which were most evident in sunny weather. 9Differences among boxes were sensitive to assumptions about bat thermal physiology and behavior. 10We found that an external water jacket mitigated temperature extremes and extended favorable temperatures into the night, which could enhance pup development while the mothers foraged. 11Further experiments are needed to evaluate the relation between metabolic heating by box occupants and thermal conditions within bat boxes.