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Information and public services for the Island of Jersey

L'înformâtion et les sèrvices publyis pouor I'Île dé Jèrri

iBats report released after 10-year study

31 October 2022

​A report analysing bat recordings logged over the past decade in Jersey has been published by the Government of Jersey and the Bat Conservation Trust. 

The report interprets the data collected through the iBatS monitoring scheme, which used mobile bat recording technology over the 10-year period. It found: 

  • The most frequently encountered bat in Jersey is the common pipistrelle (Pipistrellus pipistrellus). 
  • 99.8% of detections were those of the common pipistrelle.
  • There was an average increase of 7% per year in the relative abundance of the common pipistrelles in Jersey. This indicates that populations may be recovering. This trend has also been seen in Great Britain.
  • Most bats were found in the east of Jersey.
  • No single monitoring system will be able to provide trend data for all species in Jersey.

The report recommends several options including the use of static bat detectors to gain a better understanding of the population trends in other species. The iBatS scheme involved driving the audio detector at a constant speed along the same 11 Island-wide routes, twice a year. Each survey was done at the same time, after sunset, and when weather conditions were optimal. 

David Tipping, Senior Environment Officer for the Government of Jersey, said: “The results show that we are encountering more bat activity along these driven routes, but we don’t know to what extent this is a true reflection of the growth in the Island population as a whole. To understand more we need to look at activity in areas that aren’t accessible by car. 

“Bats are often feared, but they should be celebrated. They are hugely important and help us and our environment in many ways; they provide free pest control reducing the need for chemical pesticides, they’re critical in the pollination of many plants, and are important seed dispersers.

“There are 1,447 known species of bat in the world, 18 of which have been previously recorded in Jersey. By far the most common here is the common pipistrelle, which are often seen feeding at dusk and can hoover up around 3,000 midges and mosquitos every night. We’re lucky to have a range of other much rarer bats here too. Bats face many threats such as light pollution, roost loss and changes in the landscape. Monitoring them is therefore particularly important as they are an indicator of the health of our environment, and it informs the ways we can best protect them.”

Bat Conservation Trust Research Scientist, Dr Ella Browning, added: “We now have a much clearer idea of how Jersey’s bats are faring in the face of rapid environmental changes, thanks to the analysis of 10 years of passive acoustic survey data. This work has revealed a valuable long-term population trend for the common pipistrelle in Jersey which shows promising signs of recovery, as well as insights into patterns in bat activity across Jersey.

“Passive acoustic monitoring is a powerful tool, and coupled with a dedicated force of volunteers enables bat populations to be monitored across time and space at scales previously impossible. Although further work is needed, this report provides an important foundation for identifying effective monitoring methods and conservation actions for bats in Jersey. Gathering robust evidence on the state of biodiversity populations, such as bats, is vital if the harmful impacts of human actions on wildlife are to be reversed.” 

The research will be complemented by a further report, due later this year, looking at the data collected by a separate JBats pilot scheme which used detectors in set locations, rather than mobile recording. 

image © Hugh Clark/

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