The Secret Social Lives of Horseshoe Bats

Student Spotlight - Luke Romaine

PhD Research at Bristol University

Email: luke.romaine@bristol.ac.uk   Twitter: @lukerbio   Lab website: https://www.garethjoneslab.com/

Beady black eyes, enormous ears, and a satellite dish for a nose. Of course, I am referring to none other than the horseshoe bats. Both British species, the lesser (Rhinolophus hipposideros) and the greater horseshoe bat (Rhinolophus ferrumequinum), thrive in the West Country – favouring its warmer climes, orchards, and cattle-grazed pastures (Duvergé, 1996). It is among the honey-coloured cottages and rolling hills of the Gloucestershire Cotswolds where I find myself studying these nocturnal wonders for my PhD at the University of Bristol.

Residing in a secluded woodland valley, Woodchester Mansion is a picturesque location for my studies. The original Victorian owners failed to complete the mansion’s construction, and they never moved in. Several hundred bats did instead. In the summer, the attic maternity roost is a cacophony of shrieks and chirps as the mothers gather to give birth to their pups.

The initial bond between mother and pup is critical – it may be the most important in a pup’s life. The mothers are at their beck and call – foraging intensely over short summer nights. Moths are top of the menu and guarantee nutritious milk for high early growth rates and long-term survival prospects (Ransome, 1996, 1997, 1998). Sadly, the mother’s vital job soon comes to an end. As after around 60 days old the pups must fend for themselves (Jones et al., 1995).

Though it is the first, the maternal bond is by no means the last relationship a horseshoe bat forms during its lifetime. At two years old, some bats are mature enough to breed. From the late summer, the amorous males defend underground mating territories. If they are lucky, several females will pay a visit to pass on their genes. Some of these female groups are kin through their mother’s family line. Ultimately, this leads to the formation of closely related offspring, potentially promoting social cohesiveness in the roost (Rossiter et al., 2005). Over winter, the bats will then disperse into nearby underground systems to hibernate. Whilst many seem to favour isolation, some cluster together (Ransome, 1968).

These kinds of transient, dynamic social connections are typical of the “fission-fusion” societies we see in other bat species (Johnson et al., 2013). The structure of these connections – which other individuals one associates with, how many, when, and where – can have a big impact on survival and reproductive success. Among many individuals in a population, the emergent social structure can have profound effects on population stability and evolutionary dynamics – be it through the spread of a gene mutation, information, or disease (Kurvers et al., 2014). For the horseshoe bats in my study, many questions still remain.

For example, how durable are associations made within hibernating clusters? Are they made between close relatives, and do they have an impact on survival or reproduction? Secondly, how might mating decisions affect genetic diversity at the colony level – is it impacted by the reproductive success of different maternal lines?

Dr Roger Ransome’s tenacious research efforts over the past 64 years make my studies achievable. Using genetic data from 1993, I am piecing together a family tree, or pedigree, of the Woodchester greater horseshoe colony. It has involved many, many hours in the lab – practising and optimising my methods, extracting DNA, and performing numerous PCRs in 96-well plates. I am now near the end of determining genotypes for each individual bat. The next step will be to use this information to assign the parents for the pups born each year. Alongside this, I am performing social network analysis and thermal imaging to quantify and record the social behaviours made by the bats over winter.

The horseshoe bats are the most remarkable of our British mammals, and they continue to fascinate me. It seems the more we learn about them, the more questions arise. I am simply happy to have been given the opportunity to gain an insight into their secretive lives.

Acknowledgements

Doing a PhD amidst a pandemic has had its challenges. I’d like to thank Prof. Gareth Jones, Dr Roger Ransome, and Megan Power for their constant support over the past two years. A huge thanks also goes to Professors Darren Croft and Steve Rossiter for their continuing help with social network and genetic analysis, respectively. Thank you to the NERC GW4+ DTP for funding my studies.

References

Duvergé, P.L., 1996. Foraging activity, habitat use, development of juveniles, and diet of the greater horseshoe bat (Rhinolophus ferrumequinum-Schreber 1774) in south-west England (Doctoral dissertation, University of Bristol). https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.388116 

Jones, G., Duvergé, P. L., & Ransome, R. D. (1995). Conservation biology of an endangered species: field studies of greater horseshoe bats. Symposia of the Zoological Society of London, pp. 309–324. https://www.researchgate.net/publication/284035371_Conservation_biology_of_an_endangered_species_Field_studies_of_greater_horseshoe_bats

Johnson, J. S., Kropczynski, J. N., & Lacki, M. J. (2013). Social Network Analysis and the Study of Sociality in Bats. Acta Chiropterologica, 15(1), 1–17. https://doi.org/10.3161/150811013X667821

Kurvers, R. H. J. M., Krause, J., Croft, D. P., Wilson, A. D. M., & Wolf, M. (2014). The evolutionary and ecological consequences of animal social networks: Emerging issues. Trends in Ecology and Evolution, 29(6), 326–335. https://doi.org/10.1016/j.tree.2014.04.002

Ransome, R. D. (1968). The distribution of the Greater horse-shoe bat, Rhinolophus ferrum-equinum, during hibernation, in relation to environmental factors. Journal of Zoology, 154(1), 77–112. https://doi.org/10.1111/j.1469-7998.1968.tb05040.x

Ransome, R. D. (1996). The management of feeding areas for greater horseshoe bats. English Nature Report No. 174. English Nature, UK. http://publications.naturalengland.org.uk/publication/152012 

Ransome, R. D. (1997). The management of greater horseshoe bat feeding areas to enhance population levels. English Nature Report No. 241, English Nature, UK. http://publications.naturalengland.org.uk/publication/127051

Ransome, R. D. (1998). The impact of maternity roost conditions on populations of greater horseshoe bats. English Nature Research Report No. 292, English Nature, UK.

Rossiter, S. J., Ransome, R. D., Faulkes, C. G., Le Comber, S. C., & Jones, G. (2005). Mate fidelity and intra-lineage polygyny in greater horseshoe bats. Nature, 437(7057), 408–411. https://doi.org/10.1038/nature03965