Coping with seasons: morphological and physiological adjustments along the year in vampire bats (Desmodus rotundus) from central Mexico

Most vertebrates face seasonal variations in climatic conditions and food resources in the habitats where they live. For non-migrating small mammals, it has been proposed that primary seasonal responses to energy scarcity and low ambient temperature include reductions in body size and adjustments in thermal energetics. These predictions have been extensively tested with varied results. For example, Eptesicus fuscus , Myotis volans , and Myotis californicus reduce their body mass ( M _b ) during the most energetically demanding season of the year in central Mexico. On the other hand, Anoura latidens , a strict homeotherm from cold climates, exhibits a higher basal metabolic rate ( BMR ) and lower thermoneutral limits compared to counterparts from warmer climates. In contrast, Myotis velifer , a species capable to use torpor or hibernation, shows lower BMR and lower thermoneutral zone ( TNZ ) limits in cold environments compared to populations in warmer regions. These findings suggest that seasonal differences in thermal energetics as BMR among bats may be influenced by their ability to use torpor. In this study, we measured M _b , forearm length, and thermal energetics of Desmodus rotundus across three seasons in a tropical deciduous forest in central Mexico. We found that bats exhibited significant reductions in body size, increases in BMR and thermal conductance, decreases in critical temperatures, and a broader TNZ during the most stressful seasons of the year. These adaptations are likely driven by the bats’ inability to use torpor and two primary environmental energy constraints, 1) reduced ambient temperatures during the dry-cold season, which increase thermoregulatory energy demands, and 2) seasonal variability in livestock availability, a key energy source for D. rorundus .