Across mammals, lifespan scales with body mass: larger animals generally live longer. A shrew of comparable size to a small bat lives one or two years. Bats break the pattern comprehensively, and Myotis brandtii breaks it furthest. A male banded in Siberia was recaptured more than forty-one years after marking, making it the longest-lived bat on record relative to size.
Several features plausibly contribute. Flight and roosting in caves and crevices sharply reduce predation, which relaxes selection for fast reproduction. Deep hibernation and daily torpor lower metabolic rate for much of the year. Genome sequencing of the species found changes in growth hormone and insulin-like growth factor receptor genes, a pathway repeatedly implicated in longevity.
The trade-off is severe for conservation. Bats that live decades reproduce slowly, typically one pup a year, so a population knocked down by disease, roost loss or turbine mortality recovers over decades rather than seasons. Slow recovery, not fragility of individuals, is what makes bat declines so persistent.