Re-examining extreme sleep duration in bats: implications for sleep phylogeny, ecology, and function

Abstract

Bats, quoted as sleeping for up to 20h a day, are an often used example of extreme sleep duration amongst mammals. Given that duration has historically been one of the primary metrics featured in comparative studies of sleep, it is important that species specific sleep durations are well founded. Here, we re-examined the evidence for the characterisation of bats as extreme sleepers and discuss whether it provides a useful representation of the sleep behaviour of Chiroptera. Although there are a wealth of activity data to suggest that the diurnal cycle of bats is dominated by rest, estimates of sleep time generated from electrophysiological analyses suggest considerable interspecific variation, ranging from 83% to a more moderate 61% of the 24h day spent asleep. Temperature dependent changes in the duration and electroencephalographic profile of sleep suggest that bats represent a unique model for investigating the relationship between sleep and torpor. Further sources of intra-specific variation in sleep duration, including the impact of artificial laboratory environments and sleep intensity, remain unexplored. Future studies conducted in naturalistic environments, using larger sample sizes and relying on a pre-determined set of defining criteria will undoubtedly provide novel insights into sleep in bats and other species.

Too many men in the room? The cost of overcrowding for gregarious male cave-dwelling bats

“…Various connections have been proposed between sleep duration and social behaviour (Harding et al, 2022). The frequency of sleep that occurs consistently throughout the day is consistent with the natural circadian rhythms of bats, as they are primarily nocturnal animals.…”

“…The frequency of sleep that occurs consistently throughout the day is consistent with the natural circadian rhythms of bats, as they are primarily nocturnal animals. This dominance of sleeping behaviour among colonies may indicate the importance of rest and energy conservation within these groups after a night of activity (Harding et al, 2022;Roy et al, 2020). Bats in aggregated colonies can prioritise sleep to prepare for nocturnal activities, such as foraging and mating (Amichai et al, 2013;Harding et al, 2022;Lewis, 1996;Muñoz-Romo, 2006) and to conserve and recover energy spent on increased movement and interactions within the aggregated colony.…”

The behavioural costs of overcrowding for gregarious cave‐dwelling bats

“…Sleeping was the most frequently observed behaviour, comprising over a quarter of the total observed behaviour, and the frequency between the two groups and throughout the day was not significantly different, as this is a universally important activity for bats (Harding et al., 2022; Roy et al., 2020). The most significant difference between the two aggregations can be indicated by the significantly increased observation of negative behaviours, including aggression, movement, and wing flapping, in aggregated colonies compared with non‐aggregated ones.…”

“…Hanging relaxation was more dominant in the non‐aggregated group than in the aggregated group, indicating that solitary or loosely associated bats may exhibit a different energy allocation strategy, possibly involving increased vigilance to defend against potential threats (Harten et al., 2018; Kelm et al., 2021; Markus & Blackshaw, 2002). Sleep is the second most frequently observed behaviour in non‐aggregated bat colonies (25% of their activities; Harding et al., 2022; Lewis, 1996; Roy et al., 2020). Generally, the observed alertness in both aggregations can be associated with the presence of aggressive predators in the bat cave, which prey on bats, irrespective of roosting density (Tanalgo et al., 2020).…”

Understanding Circadian and Circannual Behavioral Cycles of Captive Giant Pandas (Ailuropoda melanoleuca) Can Help to Promote Good Welfare

“…Because of this, monitoring the amount and cycles of sleep and rest can provide insight into the affective states of species and possibly indicate positive affective states or negative ones such as boredom and disease if analyzed in the correct context [35]. For instance, prolonged rest may indicate that an animal is ill and is conserving energy to recover, but can also be suggestive of a positive affective state in a species like the little brown bat, which sleeps for approximately 20 h a day [36]. Sleep health is paramount to general welfare, and therefore, more importance needs to be placed on promoting good sleep, which can only be achieved by understanding what a healthy sleep cycle is for individuals and species.…”