When it comes to unexpected horror stories, humans may never beat nature at its scariest. In Germany, rats reportedly like to intercept bats near hibernation sites, killing and feasting on the local bat population.
Understandably, the researchers, reporting their findings in a recent Global Ecology and Conservation paper, hoped this was an “extreme scenario—a small rat population subsisting exclusively on bats.” But their investigation revealed frighteningly systematic ways in which brown rats, Rattus norvegicus, prey on the bat species Myotis daubentonii and Myotis nattereri.
If that wasn’t enough, these rats prey on bats residing in two key winter refuges for bats in northern Germany, leading the researchers to issue a strong warning for the safety of bat populations.
A nocturnal hunting spree
The investigation unfolded over several years. First, in 2020, the researchers used infrared surveillance cameras to document the rats’ behavior near the Segeberger Kalkberg, one of two caves hosting urban bat populations in northern Germany. This early observation, conducted over five weeks, chronicled 30 predation attempts and 13 confirmed kills of the bats by the rats.
Additionally, the “remains of at least 52 bats were found in a cache, clearly indicating regular feeding behavior and possibly food hoarding, as not all carcasses were fully consumed,” according to the paper.
The videos also revealed two distinct hunting strategies. While patrolling the area frequented by bats, the rats will either intercept bats midair or ambush them after they land. In both cases, the rats took distinct positions near their target, lunging forward and quickly dealing the killing bite. If the initial attack didn’t finish the job, the rats would hold the bat in place using their forelegs to deliver a second bite.
Follow-up investigations between 2021 and 2024 allowed the team to collect more evidence of rat predation on bats, including a “cache of bat carcasses” deep inside a rock near the Lüneburger Kalkberg, the other prominent bat residence.
The arrangement of the hoard closely resembled how rats had collected bat cadavers at the Segeberger Kalkberg, the researchers noted, implying that brown rats were responsible for these morbid storages as well.
The bats are not okay
Brown rats are not the natural predators of bats; it’d be more accurate to say that the rats will feast on anything available to them, the paper noted. For example, brown rats living near Japanese fish markets have a diet that is 86% fish.
What this implies is that, although bats may not constitute the entire diet for these rats, it is still possible that the bats make up a significant portion of their diet. If so, the impact of rat sieges could pose a serious threat for bat populations, which play “critical ecological roles and deliver substantial ecosystem services worldwide, including insect suppression, seed dispersal, and pollination,” the researchers added.
This unexpected interaction should also be concerning to humans, as both bats and rats are known carriers for a wide variety of pathogens—such as the coronavirus. While the paper did not specifically study pathogen transfers, it emphasized that the interactions themselves could easily become a “potential pathogen exchange between two major wildlife reservoirs.”
