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There are a large number of bats in Amsterdam's city centre. The animals live in trees, between walls and other quiet locations. Ecological consultant Jeroen Groenendijk is currently working to determine whether there are any bats at the Binnengasthuis site.

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Several years ago, the UvA conducted an assessment to determine whether the Convent and Second Surgery Clinic could serve as suitable habitats for bats in connection with the renovation of the Binnengasthuis site. 'For example, the bats can nest in cornices and cavity walls. All species of bats are protected under national and European legislation, and renovation work may not cause damage to their habitats. 

Potential habitats

According to a quick scan and a previous study, there may be bats living on the site. A follow-up study was initiated in response to these findings, and is set to be completed by the end of September. Researchers are working to identify potential bat habitats. ‘We're using bat detectors, a type of radio that can register the ultrasound calls bats make when flying and – for example – hunting for prey. Human ears cannot register these sounds, which are converted into audible signals by the detectors. We can even determine the relevant type of bat from the patterns and ultrasound frequencies. We also use flash lights,’ Groenendijk explains. The study is being conducted during the night and early morning hours. ‘You can see the bats fly to their nests at first light. There's not much point going out during cold weather, rain or wind: the bats just stay at home.'

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Pipistrelle bat photographed by: Eelco van Woersem

Key seasons

The renovation process will have to be scheduled to take into account the bats' key seasons. ‘For example, the bats' maternity season runs from May through mid-July. The females will stay together, sometimes in large groups, during pregnancy and suckling. Naturally, it's crucial not to disturb the population during this key time. The hibernation period from November through March is also an important time. Like bears, bats stockpile on food during the summer and autumn months and sleep during the winter. Their body temperature drops and their metabolism slows down, reducing energy consumption to a minimum. If we were to disrupt this hibernation period, the bats might not survive the winter months.’ 

Recommendations

Royal HaskoningDHV is advising the UvA on the necessary measures and permit applications. ‘For instance, you can make spaces unsuitable as habitats in a bat-friendly way by installing worklights. Bats don't like the light, so they simply leave. If you do this on time, they can still find another habitat - in nearby temporary bat houses, for example. The new buildings will offer space to accommodate the bat populations.’

Importance of the study

There are many different bat species. Here in the Netherlands, we have around twenty. Some of these are rare, and exclusively live in Limburg and the eastern parts of the Netherlands. Others are more common, such as the common pipistrelle bat which can also be found in Amsterdam's city centre. 
All demolition and renovation work must be scheduled to take into account the possibility of bat nests in existing buildings far in advance. This will ensure that there is enough time to identify the habitats and assess the need for measures and permit applications. A brief quick scan will generally be enough to gather the necessary information and rule out the risk of delays and high costs.