Abstract
Bats are remarkably long-lived with lifespans exceeding even those of same-sized birds. Despite a recent interest in the extraordinary longevity of bats very little is known about the shape of mortality over age, and how mortality rates are affected by the environment. Using a large set of individual-based data collected over 19 years in four free-ranging colonies of Bechstein’s bats (Myotis bechsteinii), we found no increase in the rate of mortality and no decrease in fertility demonstrating no senescence until high ages. Our finding of negligible senescence is highly unusual for long-lived mammals, grouping Bechstein’s bats with long-lived seabirds. The most important determinant of adult mortality was one particular winter season, which affected all ages and sizes equally. Apart from this winter, mortality risk did not differ between the winter and the summer season. Colony membership, a proxy for local environmental conditions, also had no effect. In addition to their implications for understanding the extra-ordinary longevity in bats, our results have strong implications for the conservation of bats, since rare catastrophic mortality events can only be detected in individual based long-term field studies. With many bat species globally threatened, such data are crucial for the successful implementation of conservation programs.
Highlights
Bats live substantially longer than non-flying mammals of similar body size[1] and group with birds in a regression of longevity on body mass[2] It is generally assumed that compared to their non-flying counterparts, species capable of active flight are better able to avoid predators, and are less prone to environmentally driven mortality[3]
How this extraordinary longevity has evolved in some taxa of bats is so far unknown
Because many species use torpor during roosting, whereby their metabolic rate can drop to one-tenth their normal rate[11], early gerontologists attributed the long lifespan of bats exclusively to this mechanism of energy saving during unfavorable food conditions[12]
Summary
Bats live substantially longer than non-flying mammals of similar body size[1] and group with birds in a regression of longevity on body mass[2] It is generally assumed that compared to their non-flying counterparts, species capable of active flight are better able to avoid predators, and are less prone to environmentally driven mortality[3] This low rate of mortality may have led to the evolution of longer lifespans by increasing the allocation of resources into somatic maintenance[3, 4]. Recent studies have confirmed that hibernating bats surpass even birds with respect to longevity[7] and no-hibernating bats live unusually long[1] Despite their small body size, the low annual reproductive output of bats puts them at the ‘slow’ end of the slow-fast continuum of mammalian life histories with high adult survival and long generation times, together with large mammals such as elephants and primates[13]. As dispersal events between different colonies are extremely rare, estimated to be approximately one female in five generations, each colony can be treated as an ecologically and demographically independent replicate[28, 32]
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