Local variations in fortunes of common pipistrelle – emerging patterns

We don’t have many conservation stories where we have seen consistent signs of the recovery of a species but we are delighted that after significant historical declines the common pipistrelle, Pipistrellus pipistrellus, has been showing a slow increasing trend and the population of common pipistrelle in Great Britain is considered to have increased since 1999 (1). We welcome the news that this remarkable species appears to be on the path to recovery thanks to legal protection and conservation action over the last few decades.

So does this mean that we can all relax safe in the knowledge that the common pipistrelle is slowly on the road to recovery? While we should celebrate the findings, we should also treat them with some caution. The national results come from a robust data set that provides valuable indicators of bat population status, change and distribution, which are then used by the Government and conservation bodies to inform conservation efforts and decision making at the national level. However, early reviews of localised patterns for common pipistrelle suggest the picture is more complicated than it would at first seem. More work is required to delve into the matter of regional and local variability, but a first analysis throws up a map for England where there are surprisingly widespread areas where the data suggest declining populations. So what might be going on here? Why might the bats in different areas be experiencing such differing fortunes? The areas appearing to show signs of decline are in the southwest, much of the south coast as well as central East Anglia, and much of northwest and north-central England. Increases are particularly evident in areas within south-east and south-central England and in some parts of East Anglia, Yorkshire, and north-west England.

Whilst the data showing these variations were not collected specifically for this purpose, they are raising some interesting questions about differences in how common pipistrelle might faring from one area to another and we want to explore this further. BCT is seeking resourcing to examine these patterns more fully and beyond that to investigate whether there is an identifiable cause and effect. Most likely candidates are the impacts of climate change, local/regional land management or a combination of the two.

So yes, the increasing national trend for common pipistrelle is strongly supported and is positive news, but the patterns suggest this is not uniform in its manifestation across England. We have much to learn or there is a danger that the slow national progress towards recovery seen in recent years could so easily and rapidly be reversed.

Common pipistrelles are long-lived mammals which reproduce slowly: each female can only produce one baby per year and not all females will have babies each year. Not all young survive the first year. For this reason their populations are very slow to grow or recover their numbers. The loss of one maternity roost site may result in all the breeding females from an area being unable to rear young in that year, and possibly future years, if there are no suitable alternative roosts nearby.

This widespread bat is the one most commonly seen flying over gardens and along hedgerows as they try to catch thousands of insects every night. While we should all welcome the news that they are becoming a more frequent sight in some areas, we need to understand why in other areas people may not be seeing them so often flying in the night sky.

Kit Stoner, BCT's CEO, said: “Legal protection and conservation action is helping common pipistrelle populations stabilise but we need to further understand why this pattern of recovery does not appear to be the same across the country. If we understand why this is we can take action to make sure this remarkable little species continues to recover and becomes more common in everyone’s night sky.”

• Bat Conservation Trust, 2022. The National Bat Monitoring Programme Annual Report 2021. Bat Conservation Trust, London. Available HERE