288-07: Population ecology and conservation of bats
Date: Tue Aug 29 14:18:16 BST 2006
Overview
We are interested in understanding the ecology and behaviour of bats, to shed light on how the natural world functions and to help conserve these endangered mammals. Our current work aims to understand two broad aspects of the ecology of bats living in temperate climates:
i) How they have evolved to thrive in a complex environment, from the spatial complexity of summer habitats to the temporal complexity of the seasonal changes in resources and resource needs.
ii) The possible consequences to bats of rapid environmental change, from habitat destruction and fragmentation to climate change.
Our ecological and behavioural data are also being used to model the epidemiology of the rabies-like virus EBL-2 which is present in Daubenton’s bats.
Why are we doing this?
We have a poor understanding of the mechanisms that determine and link behaviour, social organisation and ultimately the genetic structure of bat populations. Our understanding of the consequences to populations of mating and migration patterns is equally poor. All bats in the UK are protected by law because of their poor conservation status. Effective conservation requires a detailed understanding of an animal’s biology.
Bats are a diverse order comprising over 20% of all mammal species. Despite their small size they are long-lived mammals with complex patterns of behaviour, played out on a large landscape. Effective conservation means protecting all of their habitats: summer roosts, foraging sites, mating and hibernation sites and migration routes.
Temperate bats spend the summer in small, isolated and typically sexually-segregated colonies and we are investigating why this behaviour has evolved. Summer colonies disperse in late summer and autumn, to mate and then hibernate. About half of all European species mate at caves (or artificial underground sites such as mines and tunnels). These mating sites attract large numbers of bats from many summer colonies across large catchment areas. These sites may subsequently be used as hibemacula. Suitable sites are often a scarce and unevenly distributed resource, so bats often have to migrate over considerable distances. However, we know very little about the dispersal and migration movements of European bats.
The work involves many approaches, but all aim to enable us to study bats behaving completely naturally in the wild. However, we use two techniques that require a very small amount of tissue from some of the bats under study. To obtain this we take two 3 mm diameter disks of wing membrane (one form each wing) by a sterile, painless technique. The process takes just a few seconds and the bat is released immediately. The holes rapidly seal and heal and we continue to follow the lives of these bats for many years. The tissue is used to obtain a genetic profile of each bat, so that we can study the relationships between different populations and build a picture of population structure.
The tissue is also used for stable isotope measurements. Stable isotope analysis has become an important tool in the investigation of animal migration patterns. This is possible because stable isotope signatures in animal tissues reflect those in food webs — you are what you eat. Because signatures vary spatially in predictable ways we can map movement patterns spanning much of the annual cycle. For example, analysis of samples taken post-migration at swarming/hibernation sites will tell us where the bats spent the previous summer.
By sampling up to 50 individuals of each species from each study site we have enough material to genotype all individuals and characterise the stable hydrogen, oxygen, carbon and nitrogen profiles associated with each site. We are currently collecting samples from about 20 sites across Europe, from about eight species per site. This is the minimum required to get accurate information from genetic and stable isotope analysis.
Significance
The significance of this work is that it is a first step towards understanding bat ecology on a large spatial scale. Although most temperate bats migrate to hibernate rather than to remain active and feed, the quality of hibernation sites and the habitat along migration corridors will undoubtedly be important to summer breeding success and survival. Until now, no-one has even begun to address such issues.
Our work coincides with a Eurobats initiative (under the Convention on the Conservation of Migratory Species of Wild Animals), for a pan-European monitoring programme of underground bat sites. At a recent Eurobats workshop the need for a better understanding of bat migration to underpin this initiative was recognised.
A knowledge of migration and dispersal is also important for an understanding of how diseases that are potentially transmissible to humans may spread. Bats have been identified as reservoirs, or potential reservoirs, for a growing number of viruses, including European Bat Lyssavirus, and SARS-like coronoviruses.
The use of PIT tags
To monitor the movements of bats two techniques are currently used: ringing and radiotelemetry. To identify an individual carrying a ring we must catch the animal. Detailed information about how and why bats move roosts therefore demands regular capture and disturbance, which can alter natural behaviour. Radio transmitters provide information about roost use and feeding behaviour with no disturbance after the initial capture to attach the transmitter, but only until the battery dies or the transmitter falls off, typically after about 10 days. Subcutaneous PIT tags offer an alternative approach. Once in place a PIT tag allows us to monitor for many years, with no disturbance, the movements of bats in and out of roosts using automated readers.
