Observation of Rat Predation on Bats in German Caves

A recent study documents instances of brown rats preying on bats within caves in northern Germany, raising questions about disease transmission pathways and bat conservation. This observation occurred during research initially focused on bat communication.

Initial Discovery and Repeat Observations

Researchers filming bat swarms with infrared cameras in a cave in northern Germany observed a rat capturing and biting a bat. This event was followed by multiple similar observations, including instances where rats were able to intercept bats mid-flight. Mirjam Knörnschild, a co-author of the study and head of evolutionary diversity dynamics at the Museum of Natural History in Berlin, noted the unexpected nature of these repeated occurrences.

Urbanization and Ecological Impact

The study suggests that increasing urbanization near bat habitats, such as caves, may facilitate the presence of invasive rat populations. These brown rats are believed to originate from areas with human activity, such as a nearby open-air theater in Bad Segeberg which attracts tourists.

Further investigation in a different cave in Lüneburg, near Hamburg, revealed similar patterns, including the discovery of partially consumed bat remains. These findings indicate that rat predation on bats may be more widespread in areas with higher rat densities, often correlated with urban environments.

Knörnschild emphasized that this predation introduces an additional stressor to bat populations already facing challenges. The mechanism by which rats locate bats, despite bats' echolocation abilities, remains an area of investigation.

Implications for Disease Transmission and Conservation

Raina Plowright, an infectious disease ecologist at Cornell University, commented on the potential implications of these observations. She indicated that rats could function as a "bridging host" for bat-borne viruses, as rats frequently interact with both human and bat environments. She noted that habitat degradation associated with human expansion could inadvertently facilitate the transmission of pathogens by increasing interaction between bats, rats, and humans.

However, Plowright also stated that the current study does not indicate an immediate cause for human health concern from the specific bat populations observed, suggesting that if a pandemic-potential pathogen were present, evidence might already exist. Her primary concern is the impact on bat populations themselves, which are globally threatened by factors such as habitat destruction, noise, and light pollution. Declining bat populations could affect ecological services such as insect control, seed dispersal, and pollination.

Knörnschild's research has initiated a collaboration with Umweltbundesamt, a German federal environmental agency. The joint effort aims to develop methods for safely and humanely managing invasive rat populations in bat hibernation sites, with the goal of translating research findings into conservation actions.