BSG Ecology bat migration research (2012-2014)

BSG Ecology began research on the evidence for bat migration between the UK and continental Europe in 2012.

The research was stimulated by professional interest, which had developed as a result of bat survey work on some large sites on the east coast of the UK in the late 2000s. The data from these east coast studies appeared to show seasonal changes in bat communities potentially indicative of migration, and we therefore decided to investigate this further through research.

A summary of the evolution of our bat research, and the results from each year of work is below. Links to the detailed reports summarizing the various studies are towards the bottom of the page.

Bat Research in 2012

Initially research involved the deployment of a static bat detector at Dungeness Bird Observatory, Kent between spring and autumn: a pilot study. The aim was to establish whether there were seasonal changes in the bat community. The location was chosen due to its proximity to continental Europe, the likelihood of low levels of baseline bat use of the area (a shingle foreland characterised by fairly inhospitable habitats for bats) making changes more detectable, and because the Bird Observatory warden was happy to help us by downloading and mailing the data to us. The results were interesting, with spring and autumn peaks of Nathusius’ pipistrelle, a species known to undertake long distance seasonal migrations in Europe, and which has long been considered a likely immigrant based on records of the species on boats, oil rigs and at east coast sites where bird migration is intensively studied.

Bat Research in 2013

In 2013 we expanded our horizons a little. We remained primarily focused on Kent, due to its geographical location, and deployed bat detectors at Dungeness and Sandwich Bay Bird Observatories and at the National Trust Visitor Centre on the White Cliffs of Dover. Survey was undertaken across the entire period when bats are normally active. We also sampled other locations to add context: Spurn Point in Yorkshire, Portland in Dorset and Pilning Wetland on the Severn in Gloucestershire were all surveyed for at least part of the season. As in 2012, assistance was provided by the organisations running the sites: Bird Observatory staff, the Yorkshire Wildlife Trust and the National Trust.

The results were clear. Both individually and collectively the data for the various sites showed clear seasonal patterns of occurrence of Nathusius’ pipistrelle. These were strongly indicative of migration, with increases particularly notable in the late autumn at a time when other species (such as common and soprano pipistrelle) had long since started to decline.

To complement the static survey work, we secured samples of Nathusius’ pipistrelle fur from members of the Kent, Hertfordshire and Middlesex, North Buckinghamshire and Cardiff Bat Groups. These were taken under license from projects where Nathusius’ pipistrelles were already being captured: the groups concerned amended their licenses to allow fur sampling. Samples were catalogued and stored, and subsequently sent off for stable isotope analysis, which was conducted by Christian Voigt of the Leibniz Institute for Zoo and Wildlife Research, Berlin. The aim of this work was to establish if there was evidence that these bats had grown their fur (moulted) in different geographical regions to those they were recovered in. This work took some time, and the results are summarized under 2014 research (below).

Bat Research in 2014

In order to build on the results of previous bat survey work, and add greater certainty to our emerging (but tentative) conclusions, we took a slightly different approach in 2014.

Firstly, we deployed static detectors on ferries running between Hull (East Yorkshire) and Zeebrugge (Belgium) and Felixstowe (Suffolk) and Vlaardingen (The Netherlands) for much of the active season. We recorded Nathusius’ pipistrelle at considerable distances offshore (in the middle of the North Sea), with the timing of the encounters (spring and autumn) again indicating seasonal movements. This adds further certainty to the developing picture obtained from the east coast work that migration occurs annually, and on a relatively broad front. Thanks are due to the chief officers on the P&O vessel Pride of York and the DFDS freight vessel Flandria Seaways for agreeing to deploy the bat detectors, and to MARINELife and Envisage Wildcare for supporting the work.

Secondly, we decided to have a look at the west coast of the UK. With the support of RSPB Cymru and The Wildlife Trust of South and West Wales wardens on Ramsey, Skokholm and Skomer, we deployed static bat detectors in the spring of 2014. The aims were both to collect some baseline survey data on the bat communities of the islands, but also to look at seasonal variation potentially indicative of migration, as these islands are located relatively close to Ireland. A minimum of nine species were recorded on Ramsay and Skomer and seven on Skokholm. Some of the results were unexpected, including records of greater horseshoe bat and barbastelle, species not known to regularly cross extensive areas of water.  Others remain intriguing, such as whether changes in the number of encounters of Leisler’s bat, a species that occurs widely in Ireland, could indicate seasonal movements of bats between the UK and Ireland, passage of the species along the west coast of the UK or simply bats using the airspace for foraging.  It is clear that bats of a variety of species use the islands for foraging, and that some species are also likely to roost: a complicated picture.

The final element of research work in 2014 has been reporting the results of the Stable Isotope analysis of Nathusius’ pipistrelle hair samples collected in 2013. A total of 25 samples were analysed. The results indicated that at least 40% of the bats sampled had moved a substantial distance since they had moulted the previous summer. This strongly suggest that a proportion of the bats sampled were migratory and that, given the predominant migration direction of this species in Europe (south-west to north-east) and their known distribution in the UK, these individuals originated from areas of northern or eastern Europe outside of the UK. The sample also indicated that some of the bats sampled were resident in the UK.

Next Steps

The work undertaken between 2012 and 2014 provides strong evidence that Nathusius’ pipistrelle migrates into and out of the UK, identifies the timing of movements (which correspond with known movements in mainland Europe) and that migration appears to occur on a broad front. The stable isotope analysis results indicate that immigrants are likely to originate from north-eastern Europe, and that some populations are likely to be resident.

The work in West Wales is at an earlier stage, and conclusions cannot really be drawn on the basis of such a limited data set.  The most notable result is that both greater horseshoe and barbastelle bats have been found on the islands.

We will be considering whether to take forward further work on bat migration in early 2015. We are always happy to discuss opportunities for collaboration in relevant technical research areas.

Research Reports

The research reports can be downloaded by clicking on the links below:

Stable Isotope Analysis of Nathusius’ pipistrelle fur samples December 2014

North Sea Ferry Bat Migration Research Report 2014

Pembrokeshire Islands Bat Survey Report, December 2014

Kent Bat Migration Research Report 2013

Spurn Bat Migration Research Report 2013

Portland Bat Migration Research Report 2013

Severn Estuary Bat Migration Research Report 2013

Dungeness (Kent) Pilot Bat Migration Research Report 2012.

Further Information

For information on the work at Spurn, Portland, Severnside and on the North Sea Ferries, please contact Owain Gabb.

For further information about the Welsh Islands survey work, please contact Rachel Taylor.