Body condition is positively related to basal metabolic rate in two species of vespertilionid bats from Central Mexico

At the intraspecific level, most bat species exhibit variations in body condition. Since body condition reflects the animals’ energy reserves, as fat, and lean mass, and the size of organs, it would be positively related to the velocity at which they process energy. We measured the basal metabolic rate under laboratory conditions in Eptesicus fuscus (n = 27) (differing in body mass between 11.2 and 17.6 g), and Lasiurus cinereus (n = 18) (differing in body mass between 17.7 and 25.6 g), using open-flow respirometry, living in central Mexico. We estimated the relationship between basal metabolic rate and body condition (measured as body mass) using simple linear models. In both bat species, we found a positive relationship between these traits. Our result is likely explained by variations in metabolic active tissue and fat reserves. These differences may play a key role in natural selection of bats, affecting their energy processing and allocation strategies across different energy-spending ecological scenarios.