Flexibility in thermal physiology and behaviour allows body mass maintenance in hibernating hazel dormice

Hibernation nest site selection but not overwinter activity is associated with microclimatic conditions in a hibernating mammal

Fine-scale variation in microclimates between habitats may impact energy consumption for the organisms that inhabit them. This may be particularly important for sedentary species or those unable to change habitats for long periods, such as hibernators. Low ambient temperatures were traditionally thought key to microclimatic selection for hibernation locations, but recent research suggests that other factors may contribute or exceed ambient temperature in importance. We aimed to characterise microclimates at hibernacula of wild hibernating hazel dormice Muscardinus avellanarius, and test how these microclimates differ to those at locations without hibernacula using a microclimatic modelling approach. Dormice hibernated in areas with warmer soil temperatures and lower variability in humidity and relative shortwave radiation. These results add to the growing body of evidence that low ambient temperatures may not be the primary driver of hibernation microclimate selection, although temperature is still likely to play an important role. We also found that ambient temperatures measured at the microclimatic level were substantially buffered compared to point samples taken at the nearest weather station (∼1.6 km away), highlighting the importance of considering microclimates in wildlife conservation in the face of future environmental change.

Hibernation telomere dynamics in a shifting climate: insights from wild greater horseshoe bats

Hibernation is linked with various hypotheses to explain the extended lifespan of hibernating mammals compared with their non-hibernating counterparts. Studies on telomeres, markers of ageing and somatic maintenance, suggest telomere shortening slows during hibernation, and lengthening may reflect self-maintenance with favourable conditions. Bats in temperate zones adjust body temperatures during winter torpor to conserve energy and exploit mild conditions for foraging. Climate change may impact the hibernation cycle of bats, but more research is needed regarding the role of telomeres in understanding their response to a changing climate. Here, relative telomere length (rTL) was measured in the long-lived greater horseshoe bat Rhinolophus ferrumequinum (n = 223 individuals) over three winters, considering climatic conditions. Cross-sectional analyses revealed between-individual variation in rTL with a strong year effect, likely linked to varying weather conditions and foraging success. Additionally, within-individual increases of rTL occurred in 51% of consecutive measurements, with evidence of increasing telomerase expression during hibernation in this species. These findings highlight the beneficial effects of hibernation on telomeres and potential consequences of changing climatic conditions for long-lived temperate bats. Understanding the interplay between hibernation, telomeres, and climate can provide insights into the adaptive capacity and survival of bat populations facing environmental challenges.

Nest construction in mammals: a review of the patterns of construction and functional roles

Nesting behaviour in mammals has been investigated in a wide variety of species but to date there has not been any scholarly review of the incidence and roles of these nests. Not all mammals build nests but, while some large species regularly build nests, nest-building behaviour is more commonly associated with small mammals weighing less than a kilogram. Quantitative data for the amounts of different materials used in a nest are rarely reported but mammal nests are typically constructed from fresh (rather than dead) plant materials. Animal-derived materials seem to be rare in nests, but anthropogenic materials are reported. Few studies have examined the roles these different materials play but more physically robust materials provide support for the structure. Many mammal nests have maternity roles, but a variety of other roles were recognized. A wide range of mammalian orders use nests for resting and environmental protection. Less common roles were as sites for torpor or hibernation, or as a refuge from predation, or the materials may have anti-parasite properties. These different roles were often not mutually exclusive. It is hoped that this review will stimulate interest in the functional properties of mammalian nests. It also suggests various themes that would be interesting areas for future research. This article is part of the theme issue 'The evolutionary ecology of nests: a cross-taxon approach'.

State dependence of arousal from torpor in brown long-eared bats (Plecotus auritus)

To cope with periods of low food availability and unsuitable environmental conditions (e.g., short photoperiod or challenging weather), many heterothermic mammals can readily go into torpor to save energy. However, torpor also entails several potential costs, and quantitative energetics can, therefore, be influenced by the individual state, such as available energy reserves. We studied the thermal energetics of brown long-eared bats (Plecotus auritus) in the northern part of its distributional range, including torpor entry, thermoregulatory ability during torpor and how they responded metabolically to an increasing ambient temperature (Ta) during arousal from torpor. Torpor entry occurred later in bats with higher body mass (Mb). During torpor, only 10 out of 21 bats increased oxygen consumption (V̇O2) to a greater extent above the mean torpor metabolic rates (TMR) when exposed to low Ta. The slope of the torpid thermoregulatory curve was shallower than that of resting metabolic rate (RMR) during normothermic conditions, indicating a higher thermal insulation during torpor. During exposure to an increasing Ta, all bats increased metabolic rate exponentially, but the bats with higher Mb aroused at a lower Ta than those with lower Mb. In bats with low Mb, arousal was postponed to an Ta above the lower critical temperature of the thermoneutral zone. Our results demonstrate that physiological traits, which are often considered fixed, can be more flexible than previously assumed and vary with individual state. Thus, future studies of thermal physiology should to a greater extent take individual state-dependent effects into account.