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Acoustic romance in old church attics: Greater mouse-eared bats display lek mating system

In the darkness of old church attics, surprisingly romantic scenes take place as male greater mouse-eared bats (Myotis myotis), the largest native bat species in Europe, compete for the attention of females using complex vocalizations and remarkable patience.

A new study from the Museum für Naturkunde, in the Annals of the New York Academy of Sciences, provides novel insights into the mating behavior of these bats, revealing that Myotis myotis exhibits a lek mating system—a strategy rarely documented in bats.

As part of her doctoral research, Lisa Printz observed more than 70 male Myotis myotis in the attics of six churches. She found that the males occupied small, repeatedly used roosting spots within the attic and defended them against rival males. Through complex trill vocalizations, the males fend off competitors and court nearby females.

This collective yet competitive gathering of males in specific display areas is known as a "lek." Females travel considerable distances to reach these sites during the mating season and the males compete for the favor of visiting females.

"For the first time, we were able to document in detail that the Greater Mouse-eared bat exhibits a lek mating system—a mating system previously confirmed in only a few bat species," explains Printz. "Despite the mating, males offer no resources to the females and compete solely for the attention of the females."

Males show increased site fidelity to their roosts from the beginning of June, which is reflected by heightened territorial behavior. Interestingly, the arriving females seem to make their choices even before landing, flying directly to a specific male.

Even the mating behavior itself is surprising. After a female lands beside her chosen male, the mating pair will often rest quietly side by side before the mating event begins. In many cases, the male wraps his wings around the female after copulating, and the pair remain in close contact before copulating again. The longest recorded mating session lasted over 34 hours.

"This prolonged mating event and subsequent resting period might represent a form of mate guarding," suggests Dr. Mirjam Knörnschild of the Museum für Naturkunde Berlin. "It may help ensure successful reproduction."

The findings have significant implications for conservation efforts. Male Myotis myotis show strong fidelity to their roosting sites. Renovation or structural changes to buildings such as churches or monasteries could seriously disrupt the mating season.

"So far, the general assumption is that males are more flexible than females, which is why male roosts haven't received much attention in conservation strategies," says Printz. "However, our results show that males also use specific roosts seasonally and show long-term fidelity to their traditional roosting sites."

This study improves our understanding of the mating behavior of a widespread European bat species and calls for a re-evaluation of current conservation practices. The authors argue that male roosts should be protected just as carefully as maternity roosts and hibernation sites, by targeted conservation strategies and the preservation of male display spots.