Increase in bat numbers in the winter roost

Bat conservationists have been taking advantage of the cold weather to count the winter roosts of greater mouse-eared bats and other species. It was the first count in the Frankfurt Ostquell Brewery since the completion of the renovation work – and the results were very encouraging.

In search of the bats in the vaults of the old Ostquell Brewery.

© Krzysztof Gajda
Daubenton's bat during hibertination

While the greater mouse-eared bat is very sociable and forms large clusters in winter, hanging upside down from the ceiling, other species like this Daubenton's bat prefer to spend the cold season on their own. The motto here is: the closer the hiding place, the more readily it is accepted.

© LPV Mittlere Oder e.V.

1,695 bats are spending this winter in Frankfurt on Oder, in the vaults of the former Ostquell Brewery, owned by EuroNatur. The most regular guest to this “bat hotel” is once again the greater mouse-eared bat with almost 600 individuals. This is followed by the Natterer’s and Daubenton’s bats. This was the finding of a survey carried out by volunteers on January 14th.

For many years these insect-eating mammals have been using the frost-free and undisturbed cellar vaults in Frankfurt as a winter roost. Since the ruin was on the verge of total collapse, we had been carrying out renovation work every summer over the last three years. The holes in the roof were repaired and new supporting columns fitted to stabilise the roof structure. In some of the rooms in the maze of cellars, the walls have been sealed to protect the bats from the frost. Whilst bats like it cool, minus temperatures can quickly kill them. In addition, other hiding places such as cracks were created.

All these measures have clearly proved popular with the bats. These figures represent the highest hibernation numbers in the last seven years (there was no count in 2021 because of Covid). Whilst the numbers of greater mouse-eared bat have stayed almost constant, the figures for Natterer’s and Daubenton’s bats have jumped. Even the brown long-eared bat with 24 individuals has recorded the highest value for over 10 years. The renovation measures are thus proving successful.

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