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.

bat conservationists in the Old Brewery

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

© Krzysztof Gajda

Whereas the greater mouse-eared bats are very sociable and form big clusters in the winter, hanging upside down from the ceiling, other species prefer to spend the cold season of the year by themselves. The rule here is: the more cramped the hiding place, the more likely it is to be accepted by the bats.

© LPV Mittlere Oder

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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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…