Bats on a break: tracking the secret life of pond bats

A pond bat from the study with a GPS tag on his back.
Photo Credit: René Janssen

Scientific Frontline: Extended "At a Glance" Summary: Pond Bat Nocturnal Behavior and Functional Habitat Use

The Core Concept: A novel ecological study reveals that vulnerable pond bats spend approximately one-third of their active night resting outdoors, highlighting the critical need to preserve mixed-habitat landscapes to support both foraging and resting behaviors.

Key Distinction/Mechanism: Unlike previous tracking methods that solely mapped geographical locations, this research utilizes 1.2-gram GPS loggers equipped with built-in accelerometers. This mechanism allows scientists to identify distinct behavioral states (active versus resting) and link them directly to specific environmental features, an approach defined as "functional habitat use."

Major Frameworks/Components:

• Functional Habitat Use: A spatial ecology framework that connects distinct animal behaviors to specific environmental requirements.
• Foraging Zones: High-density, vegetation-rich edges along lakes, ponds, and rivers that yield abundant insect prey.
• Commuting Corridors: Straight waterways, such as canals, which function as transit "highways" between daytime roots and feeding grounds.
• Nocturnal Roosting Sites: Forest edges and isolated trees near water bodies, which accommodate the limited maneuverability of these fast-flying bats during feeding breaks.

Branch of Science: Ecology, Environmental Biology, Zoology (specifically Chiropterology), and Conservation Science.

Future Application: The combined GPS and accelerometer tracking methodology can be deployed in future studies across different regions and bat species. The findings provide a blueprint for urban planners and conservationists to protect interconnected landscape elements rather than focusing solely on isolated daytime roosts.

Why It Matters: Pond bats (Myotis dasycneme) are classified as vulnerable on the IUCN Red List, driven by habitat loss, declining insect populations, and the loss of roosting spaces due to modern building insulation. Formulating conservation policies that protect the full spectrum of their nocturnal habitat needs is essential for preventing further population decline.

Capturing pond bats in Rotterdam.
Photo Credit: René Janssen

What do bats do at night when they’re not hunting? Using tiny GPS trackers, Leiden researchers discovered that pond bats spend a substantial portion of the night resting – often outdoors. This surprising insight could change the way we protect them. 

Over a narrow waterway beneath a bridge, a fine mist net hangs in the dark. Volunteers wait quietly throughout the night. Then, suddenly, a soft flutter. Now, the volunteers have to act quickly. 

This is how the fieldwork of a new pilot project on pond bats (Myotis dasycneme) started. Environmental scientist Yali Si calls it a real ‘passion project’, carried out in Leiden and Rotterdam, in collaboration with master students, NGOs, and other conservation partners (see below). 

For the first time, researchers fitted pond bats with GPS loggers combined with motion sensors, offering an unprecedented glimpse into their nocturnal lives. 

Vulnerable species 

According to the IUCN Red List of threatened species in 2023, Pond bats are considered vulnerable across Europe. Their populations are declining due to habitat loss, decreasing insect (prey) numbers, and modern building insulation reducing roosting spaces. 

Not only seeing where they are, but also what they’re doing 

The devices are tiny, just 1.2 grams, but powerful. ‘We don’t just see where they are, but also what they’re doing,’ Si explains. ‘With accelerometer data, we can tell whether a bat is active or resting.’ 

That combination is key. Previous studies mostly mapped locations, but this new approach links behavior to specific habitats. ‘We call this functional habitat use: different parts of the landscape serve different purposes, like foraging or resting.’ Until now, that part has been largely overlooked. 

Pond bats rest outdoors at night 

For a long time, where pond bats rest during the night remained largely unknown—especially outdoors. Tracking data now shows that they spend about a third of their time resting between feeding bouts. During these breaks, they mainly hang in trees along forest edges or in isolated trees near water, and only occasionally in buildings. 

This makes sense: pond bats forage over water, catching insects. Si explains: ‘They need places to hunt but also places to rest in between. Ideally, these are close together.’ 

A landscape that supports bats 

‘These new insights show why it’s important to look beyond day roosts and foraging areas,’ Si explains. ‘You need to think about the whole landscape.’ Beyond Leiden and Rotterdam, the methods from this study can guide future research in other regions, or other bat species, helping scientists understand how different habitats within the landscape support these key behaviors. 

Around Leiden and Rotterdam, pond bats rely on a mix of habitats: High-density; vegetation-rich edges along lakes, ponds, rivers and waterways provide abundant insects for feeding. Straight waterways, like canals, serve as commuting ‘highways’ between their daytime roots and the feeding spots. For resting during the night, pond bats mainly depend on forest edges or isolated trees close to foraging waters, as they are fast flyers that are less maneuverable in dense forests. 

Protecting this combination of habitats across the landscape is key to supporting both their feeding and resting needs – the foundation for effective conservation. Sometimes, even for bats, a quiet rest is all you need. 

Additional information: A large part of the work was carried out by master’s student Gijs van der Velden who wrote his master’s thesis on the project. His work earned the Stans Award for the Best CML Students Thesis. Si praises Van der Velden’s commitment and quantitative skills, and the way he collaborated with the partners. 

Funding: Funded by the CML Biodiversity Programme and Zoogdierwerkgroep Zuid-Holland and Gemeente Rotterdam 

Published in journal: Biological Conservation

Title: To rest or to roam: Functional habitat use of an insectivorous bat species during active and resting behavior

Authors: Gijs van der Velden, Bart Kranstauber, Anne-Jifke Haarsma, René Janssen, Mees van Horssen, Wouter Halfwerk, Anton van Meurs, Cynthia Bom, Maarten Schrama, Yali Si

Source/Credit: Leiden University

Reference Number: eco041426_01

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