Body Size Decline in an Endangered Bat Is Associated With Climate Change at a Continental Scale but Varies by Phenophase and Region

Abstract

At high latitudes, hibernating species must replenish their energy reserves within a 4–6 month active season. During this window, insectivorous bats at higher latitudes must consume sufficient arthropod prey to support reproduction and migration, despite suboptimal weather and prey abundance that varies across time and space. Local declines in body size of endangered little brown bats ( Myotis lucifugus ) suggest ongoing nutritional stress associated with limited prey availability and inclement weather. We tested the hypothesis that climate change has caused nutritional stress in bats at a continental scale. We analyzed morphometric data from > 21,000 bats from five regions across Canada and northern Montana over 8–16 years. We used forearm length as a proxy for access to nutrition during development, and body mass as a proxy for recent energy reserves. Average adult and juvenile forearm length declined over time in most study regions, although the magnitude of the estimated declines varied geographically. We found that the interactive effects of rainfall and temperature on reproductive females exerted a carry‐over effect on juvenile body size, as juvenile forearm length was shorter, on average, in years when mothers experienced poor weather before and after hibernation. Although changes in adult body mass were geographically widespread, the drivers, direction, and magnitude of these trends varied among phenophases, demographic groups, and study regions. This result implies the effects of other, stochastic factors, such as arthropod abundance or wildfires, although these cannot be directly tested with the available data. Our study illustrates that directional changes in average temperature and rainfall can affect the energetics and development of little brown bats. Ongoing nutritional stress associated with climate change may impact the viability of bat populations that are also threatened by white‐nose disease.

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