Research Group 1: Evolutionary Ecology

EUROPEAN BAT MIGRATION PROJECT

1. Tracing bat migratory routes through the isotopic fingerprint in hairs
2. The techniques
3. Implementation
4. Our team
5. Join the Project!

Tracing bat migratory routes through the isotopic fingerprint in hair 

Among the many fascinating attributes of bats is their potential to migrate. Although all European bats are included under the Convention on Migratory Species (Bonn, 1979), only four species are accepted to perform long-distance migrations comparable to those of birds: the parti-coloured bat Vespertilio murinus (1), the common noctule Nyctalus noctula (2), Nathusius’ bat Pipistrellus nathusii (3), and the lesser noctule Nyctalus leisleri (4). Other species, such as the giant noctule Nyctalus lasiopterus (5) who preys on migratory birds, are still too unknown for us to judge their migratory capacity. Which bat species are long-distance migrants in Europe? Even for those bats widely recognized as migrants, the difficulty to get recovery data of banded individuals renders our picture of bat migratory routes in Europe much too inaccurate. Many areas across Europe receive seasonal visits of bats, sometimes arriving in large numbers, which disappear later as mysteriously as they arrived. Where do these bats come from and where are they heading to? Sometimes, certain individuals settle down in an area, while other individuals of the same species travel away to distant lands year after year. Why do migratory bats migrate, and why don’t they always do so? In certain occasions, males of a certain bat species can be found in an area throughout the year but females only show up at a certain season. Is migratory behavior of bats sex-specific or sex-biased? Saddest of all, our efforts to protect migratory bats in our respective nations will be useless if the same animals are threatened at their other residency areas. How can we join our efforts to protect our trans-European bats efficiently? Understanding where, how and why bats migrate is a necessary step towards predicting how current changes related to global warming will affect their distribution range, behavior and the survival of their populations. What future challenges await our migratory bats in the face of current global change?

These are the questions that we want to answer through the creation of the European Bat Migration Project. To fulfill this goal, we count with the invaluable support of a network of bat researchers across Europe and with the promising technique of water isotope analysis in hair.

The technique

Because of global hydrological processes, stable hydrogen and oxygen isotopes present in precipitation and ground water form large-scale gradients in continents [see www.waterisotopes.org], constituting excellent geographical markers that have been used in a broad amount of applications. These isotopes pass on to the plants that absorb this water, or to the animals that drink it.

Bats molt their hair only once a year, during or after the breeding season. For migrating bats, this energy-consuming process takes place before migration, still at the breeding areas. The hydrogen and oxygen isotopes incorporated into the new formed hair contain a signature of the water present in the breeding area. This signature will be carried around by the bat all along its migratory travel, and will not be renewed until the next molt takes places one year later, back at the summer quarters.

All migratory bats are forest bats, that is, they roost mostly in tree cavities (right, common noctules inside a tree hole), which are poorly isolated in comparison to caves or man-made buildings. For this reason, they are forced to travel towards regions of milder climate during winter if they want to avoid freezing inside their hibernating tree holes. Many migratory bats have been killed or have lost their natural roosts due to logging of mature  or rotten trees, their favorite roosts (left, the remains of a gallery forest).

 Bats captured on migration or after they have arrived at their wintering grounds will therefore carry in them a fingerprint of their breeding areas that can be revealed by analyzing hydrogen and oxygen isotopes in their hair.  This fingerprint will differ from that of sedentary bat species, or sedentary individuals of the same species, which on the contrary will reflect local water isotopes.

Bat species considered to be sedentary, such as this Plecotus auritus on the left and Myotis nattereri (now the Iberian M. escalerai) on the right, will be sampled as reference for creating contour maps of hydrogen and oxygen isotopes in bat hair across Europe.

Contrasting our data with available maps of water isotope patterns in Europe and with maps of hair isotopic values that we will create for sedentary bats in Europe, we shall be able to:

Assign migratory bats captured in migration or at hibernacula to breeding areas

• Identify differences in migratory paths in Central-West (mostly northeast-southwest direction) and East Europe (with hypothesized north-south direction)

• Clarify the migratory status of dubious species

• Discuss our results in an international, intra-European collaborative network to design joint conservation measures for migratory bats and to elaborate predictive models of bat migratory patterns in the future Europe

Implementation

This project would not be possible without the voluntary work of bat researchers all over Europe who are collecting hair samples of sedentary and migratory bats from their countries.  We still need to find more collaborators in East European countries, especially Russia and Turkey!! Bats will be sampled in spring, prior to the breeding season, and in autumn, prior to hibernating. Hair samples will be analyzed at the stable isotope laboratory of the IZW.

Several methods can be employed for capturing migratory bats. The simplest and most convenient is taking them directly from the roosts (as A. Popa-Lisseanu on the left). When the roosts are known but removal from the roosts is not possible, a mist-net can be installed to intercept the way out of the bats at emergence (center, a giant noctule has been captured after leaving its roosts under the leaves of a palm tree). If no roosts are known, mist-netting can be done in ponds or streams to capture drinking bats (on the right, C. Ibáñez and P. Agirre-Mendi are setting up mist-nets in a pond in La Rioja, Northern Spain).

Frau Sörensen is our  brand-new Delta V IRMS (Thermo Finnigan MAT). She will be in charge of analyzing hydrogen and oxygen isotopes in bat hair (left). Only a small amount of hair (0.1 - 0.3 mg) is necessary for the analysis (right). 

Our team

Join the Project!

For more information about the project and detailed instructions for sample collection in the field, the following files are available for download:

Batmigeu_description.pdf

Fieldprotocol.pdf

Fielddatasheet.pdf 

For comments and suggestions, or if you wish to collaborate in this project, please contact Ana G. Popa-Lisseanu at
anapopa@ebd.csic.es  or at 00 49 (0)30 5168 513