Rapidly declining body size in an insectivorous bat is associated with increased precipitation and decreased survival

Abstract

Reduced food availability is implicated in declines in avian aerial insectivores, but the effect of nutritional stress on mammalian aerial insectivores is unclear. Unlike birds, insectivorous bats provision their young through lactation, which might protect nursing juveniles when prey availability is low but could increase the energetic burden on lactating females. We analyzed a 15-year capture-mark-recapture data set from 5312 individual little brown myotis (Myotis lucifugus) captured at 11 maternity colonies in northwestern Canada, to test the hypothesis that nutritional stress is impacting these mammalian aerial insectivores. We used long-bone (forearm [FA]) length as a proxy for relative access to nutrition during development, and body mass as a proxy for access to nutrition prior to capture. Average FA length and body mass both decreased significantly over the study period in adult females and juveniles, suggesting decreased access to nutrition. Effect sizes were very small, similar to those reported for declining body size in avian aerial insectivores. Declines in juvenile body mass were only observed in individuals captured in late summer when they were foraging independently, supporting our hypothesis that lactation provides some protection to nursing young during periods of nutritional stress. Potential drivers of the decline in bat size include one or both of (1) declining insect (prey) abundance, and (2) declining prey availability. Echolocating insectivorous bats cannot forage effectively during rainfall, which is increasing in our study area. The body mass of captured adult females and juveniles in our study was lower, on average, after periods of high rainfall, and higher after warmer-than-average periods. Finally, survival models revealed a positive association between FA length and survival, suggesting a fitness consequence to declines in body size. Our study area has not yet been impacted by bat white-nose syndrome (WNS), but research elsewhere has suggested that fatter bats are more likely to survive infection. We found evidence for WNSindependent shifts in the body size of little brown myotis, which can inform

Apparent annual survival of female eastern small-footed bats (Myotis leibii) roosting in Arkansas bridges

“…bats, such as Little Brown Bat ( M. lucifugus ; 0.63–90; Frick et al 2009) and Indiana Bat (0.627; Boyles et al 2007) but similar to average adult female survival (0.774) derived from multiple species (Lentini et al 2015). Studies of insectivorous bats typically find survival of juveniles during their first year lower than adult survival (Frick et al 2009; O'Shea et al 2010; Lentini et al 2015; Davy et al 2022), similar to the results of this study. Our survival rate of juvenile females (0.472) was generally greater than those reported for other Myotis spp.…”

Early successional habitats created through plantation harvesting benefit the Gray Nightjar (Caprimulgus jotaka): An 8-year survey in central Hokkaido, northern Japan

“…By contrast, no elevation effect on nightjar occupancy was detected in a previous study conducted in warmer regions of Japan (Yamaguchi and Mitarai 2018); thus, our results were likely a reflection of temperature effects. The negative impacts of cool conditions have been reported for nocturnal insectivores (European Nightjar: Morris et al 1994, bats: Rydell et al 1996Davy et al 2022). There are two possible explanations for this finding.…”

Long‐term exposure to an invasive fungal pathogen decreases Eptesicus fuscus body mass with increasing latitude

“…Anthropogenic changes in the environment that alter insect prey populations, such as climate change and insecticide use, could have played a role in altering E. fuscus body mass with Pd exposure time-steps (Wagner, 2020). Declines in available insect prey and the nutrition quality of insect prey have also been suggested to contribute to declines in other temperate bat body conditions over time without Pd infections (Davy et al, 2022). All female demographics and male bat body mass decreased with latitude by Pd establishment, and differences between northern and southern bat mass progressively increased.…”