Bat population recoveries give insight into clustering strategies during hibernation
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RESEARCH
Open Access
Bat population recoveries give insight into clustering strategies during hibernation Natália Martínková1,2*
ˇ 3 and Jan Zima1 ˆ , Stuart J. E. Baird1 , Vlastislav Kána
Abstract Background: Behaviour during hibernation contributes to energy conservation in winter. Hibernating bats select roosts with respect to physiological and environmental stressors, available local microclimate and species-specific requirements. Results: We found that, in the period between 1977 and 2018, hibernating Myotis myotis and Rhinolophus hipposideros bats showed exponential population growth. The growth rates, corrected for local winter seasonal severity and winter duration, were equal to 10 and 13%, respectively. While R. hipposideros only utilised the thermally stable and, at survey time, warmer corridors in the hibernaculum, an increasing proportion of M. myotis roosted in the thermally stable corridors as their abundance increased. About 14% of all hibernating M. myotis displayed solitary roosting, irrespective of other covariates. Those bats that clustered together formed progressively larger clusters with increasing abundance, particularly in cold corridors. We found no statistically significant relationship for clustering behaviour or cluster size with winter severity or winter duration. Conclusions: Abundance of hibernating bats is increasing in Central Europe. As the number of M. myotis bats increases, thermally unstable corridors become saturated with large clusters and the animals begin to roost deeper underground. Keywords: Chiroptera, Hibernation, Population size, Clustering behaviour, Winter activity
Background Bat species in the temperate zone hibernate to save energy during the winter, when food is unavailable and environmental conditions are unfavourable. Hibernating animals in torpor reduce their metabolism, lower their body temperature close to the ambient temperature, slow their heart rate and breathing frequency, and modulate the immune response [1, 2]. To reduce exposure to outside environmental conditions and predation risk, animals use natural caves, artificial galleries, cellars and other suitable places in buildings, rock crevices or hollow trees as shelters. *Correspondence: [email protected] ˆDeceased Institute of Vertebrate Biology, Czech Academy of Sciences, Kvˇetná 8, 60365 Brno, Czechia 2 RECETOX, Masaryk University, Kamenice 753/5, 62500 Brno, Czechia Full list of author information is available at the end of the article 1
The phenology of hibernation is a species-specific endogenous process linked to the photoperiod, sex, age and local weather with great phenotypic plasticity [3, 4]. As a result, individuals enter hibernacula over a period of several weeks, when their numbers on site fluctuate markedly and individual torpor bouts are short [5–7]. Towards the end of hibernation, a similar activity occurs, bats change roosts in hibernacula more frequently, move closer to the entrance of underground spaces, and might emerge on warm nights [8, 9]. The direction of draught at the hibe
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