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2012/1/4

The Bechstein’s bat, more Mediterranean than thought

The Bechstein’s bat or Myotis bechsteinii lives in deciduous forests. It used to be very common in the Holocene era, but today there are only a few dispersed groups, despite the fact that a colony can be found almost anywhere in Europe. It has been rendered vulnerable by human interference and forest destruction. And this has even led to confusion about its origin, as the biologist María Napal has shown. In fact, the natural habitat of the Bechstein’s bat is said to be Central Europe, but the results produced by this researcher point to the Mediterranean: even though it is true that this species is less common in this area, the reason for this is not that they are strangers to its bioclimatic conditions, but that their forests are disappearing. Napal did her thesis, entitled Comparative study of Bechstein’s bats in contrasting climates: the legacy of forest transformations, at the University of the Basque Country (UPV/EHU). 

The starting point of this piece of work is the paradox discovered in the Iberian Peninsula. The data indicate that there is in fact a high density of Bechstein’s bats in some Mediterranean areas. By contrast, it is difficult to find them in the Atlantic area, even though the climate there is more similar to that of Central Europe. So Napal concludes that the reduced presence of the species in the south of Europe cannot be attributed to warm bioclimatic conditions. There must be another reason, because if not, there would be more of them in Galicia than, for example, in Andalusia. “We realised that the Mediterranean areas were no worse for the species. And that this bat could have originated in the Mediterranean, but due to the destruction, the forests receded towards the continent; and so did the species together with the forests,” says Napal. And she highlights the need to re-analyse its ecological requirements.  

Nothing wrong with heat 

Not only are the Mediterranean conditions not harmful, they are, as the researcher has shown, beneficial for the survival of the species: “Life is easier in the Mediterranean area than on the Atlantic seaboard. The climate is not so harsh, and the bats do not need to cope with such strict conditions.” Thanks to the warmer temperatures, the southerly Bechstein’s bats are more flexible when deciding which trees they are going to use for roosting.

So the problem is not the climate, but the decline in the forests caused by the evolution of nature and, above all, by the interference of human beings. These bats have very limited, dispersed roosting places in the Mediterranean area and throughout the Iberian Peninsula. “This bat has a very limited capacity to move around; barely a kilometre per day from its roosting place to the hunting areas. If the forest is not a very dense one, the bat finds it quite difficult to move from one place to another, and that is why the population suffers from isolation. This can lead to harmful genetic and demographic consequences,” says Napal.

For example, as verified in her thesis, the Bechstein’s bat population in Cazorla (Andalusia) is showing signs of genetic impoverishment. However, the researcher stresses that the actual problem is the isolation in itself. It is a fact that the Mediterranean variety is totally cut off and its population has few options for growth in comparison with that of Central Europe. Likewise, the destruction or breaking up of the forests and the isolation resulting from this also shed some light on understanding the limited presence of this bat in the Atlantic area, since human activity there has been continual in recent years.   

Proposals

In generic terms and however much better the situation in Central Europe may be, Napal is not particularly optimistic as far as the Bechstein's bat is concerned. Its decline since the Holocene era up until today has been well known, and much more so since human beings have been exploiting the forests: “It is clear that the species is in decline. If the forests are preserved or increased, this species could recover, but this is very difficult because, as we have pointed out, it has a limited capacity for movement and reproduction.”

In this respect, some proposals for preserving it are put forward in the piece of research. These include keeping a few mature trees in each forested area so that the bats can use them for roosting; introducing more deciduous trees in the Mediterranean basin; guaranteeing sources of water; and ensuring the continuity and heterogeneous structure of the forests.

About the author

María Napal-Fraile (Estella, Navarre, 1983) is a graduate in Biology. She wrote up her thesis under the supervision of Joxerra Aihartza Azurtza, who belongs to the Department of Zoology and Animal Cellular Biology of the Faculty of Science and Technology at the UPV/EHU; that was where she defended her work. Napal did her research mainly at the UPV/EHU, but also spent three months (August-December 2010) in Germany at the Max Planck Institute for Ornithology (at Seewiesen near Munich).

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