Abstract
Changes in environmental conditions can have strong energetic effects on animals through limited food availability or increased thermoregulatory costs. Especially difficult are periods of increased energy expenditures, such as reproduction. Reproductive female bats from the temperate zone often aggregate in maternity colonies to profit from social thermoregulation to reduce torpor use and buffer the effects of poor conditions. The much rarer male colonies may form for similar reasons during testes development. Male colonies thus allow us to study the influence of environmental conditions on energy budget and colony size, without the confounding effects of parental care. We remotely monitored skin temperature and assessed colony size of male parti-coloured bats Vespertilio murinus during summer, and correlated those variables with environmental conditions and food availability (i.e. insect abundance). As we had hypothesized, we found that colony size increased at colder temperatures, but decreased at low wind speeds. Also as predicted, torpor use was relatively low, however, it did increase slightly during adverse conditions. Male sociality may be an adaptation to adverse environmental conditions during sexual maturation, but the pressure to avoid torpor during spermatogenesis may be lower than in pregnant or lactating females.
Highlights
Environmental conditions such as temperature, humidity, salinity, or photoperiod, have a strong influence on all living organisms
Relationship between bat Social warming and the use of torpor are alternative mechanisms of energy conservation bats use under poor weather conditions (Speakman and Thomas 2003; Willis and Brigham 2007), that have been observed in pregnant, lactating as well as non-reproductive females and males (Lausen and Barclay 2003; Dietz and Kalko 2006; Pretzlaff et al 2010; Dzal and Brigham 2013; Johnson and Lacki 2014)
We provide an assessment of behavioural and physiological strategies of how male bats deal with adverse environmental factors
Summary
Environmental conditions such as temperature, humidity, salinity, or photoperiod, have a strong influence on all living organisms. Small endothermic animals with their high surface to volume ratio and often high metabolisms, can be affected by seasonal or even daily fluctuations in conditions strongly (McNab 1983; Boyles et al 2007; Boratyński et al 2018). This is especially pronounced in small insectivorous mammals, because short-term changes in weather impact them directly, and through their effect on insect occurrence. The resulting large fluctuations in insect availability require corresponding adaptations by insectivorous animals to balance their energy budget. During energetically costly reproduction (Lane et al 2010) bats have to increase caloric intake while they reduce use their main energy saving strategy, torpor, as it interferes with foetal development, milk, and sperm production
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