Natterer's bats in churches research
2012-2014, University of Bristol
Natterer’s bats occasionally form large maternity colonies in churches where their urine and droppings can cause problems. To address these issues and find practical solutions, two research projects were undertaken by the University of Bristol.
The research was designed to show whether encouraging bats away from sensitive areas in churches can be achieved in a practical and ecologically sound manner. It should be stressed that this research took place under licence, as the use of such techniques to disturb bats would otherwise be illegal.
Natterer’s bats tend to fly within the body of the church where they can deposit urine and droppings. This can cause damage to furnishings and fittings which is a special concern if these are irreplaceable objects of national or international significance as is often the case in historic churches.Large quantities of droppings can also restrict the use of a church for worship or other community functions when the burden of maintenance becomes unmangeable.
Successful solutions needed to be built on a clearer understanding of why Natterer’s bats select churches as roosts, how they use the building and how their use of affected church buildings could be altered. The University of Bristol drew on the expertise of a number of partners to determine the roosting requirements of this species and evaluate management options that could help church users, at the same time as supporting the conservation of this protected species.
Funded by DEFRA, the project aims were...
To engage a variety of stakeholders to ensure the research is relevant and gather feedback on the possible options
To determine the key features of current roosts to inform the creation of effective alternative roost sites
To develop options that allow bats to remain within churches but reduce the impact of bat droppings and urine in sensitive areas
To assess the impact of management actions, taken to deter bats or limit the damage they cause, on the welfare of the local bat population
To determine the impact of the management actions taken on local bat populations and model likely population trends
What we learned...
The radio-tracking studies of Natterer’s bats that were undertaken throughout the research project showed that the colonies studied were highly dependent on their church roosts with little use of other roosts in the local area. This demonstrated the importance of understanding how an individual bat colony uses a church when attempting to manipulate its behaviour.
In the short-term trials in 2012, the use of a sound deterrent appeared to be effective at preventing bats from using their original roost within the church during the four days of the trial and bat droppings collected below the original roosts typically reduced to zero by the third or fourth day of deterrent use. They found no evidence that the use of this acoustic deterrent affected the foraging behaviour of Natterer’s bats.
At the churches that undertook extended trials of the acoustic deterrents, the bats quickly relocated to alternative roosting locations within the church. There was no evidence that the bats habituated to the deterrents during their 15-days of operation. The use of the deterrents did not appear to result in the bats leaving the churches altogether over the period as similar numbers of bats were present throughout the trial, but they did move to roost in different locations within the church.
The use of directed artificial lighting substantially reduced bat flight activity in lit areas of churches for all bat species, but due to negative impact on foraging behaviour and risk of bats refusing to leave their roosts at all, light deterrents were not deemed a viable solution. The response of Natterer’s bats was particularly strong with common and soprano pipistrelle species less affected. The lighting was also observed to change the emergence and nocturnal activity of Natterer’s bats, time of emergence became more variable and the length of time the bats spent foraging outside the church was reduced. The use of lighting over extended periods is likely to be detrimental to bat welfare and conservation.
There was little evidence that bat boxes installed inside and outside the churches had been used by bats during the study’s experimental periods, but droppings underneath the boxes suggest some have been used subsequently. It has been observed in other mitigation studies that it may take a number of years before artificial enhancements such as boxes are used. Within churches, bats may choose to use other alternative known roosting locations in preference to these newly installed features.