# Summer and Autumn Activity of Eptesicus nilssonii and Other Bat Species in a High-Altitude Ice Cave in the Tatra Mountains (Southern Poland)

## TL;DR

This study shows that high-altitude ice caves in the Tatra Mountains are important for northern bats and other species during summer and autumn, especially for mating.

## Contribution

The study reveals that high-altitude ice caves are crucial mating and swarming sites for Eptesicus nilssonii in a warming climate.

## Key findings

- Eptesicus nilssonii was the most abundant bat species at the cave, showing consistent activity from June to November.
- Swarming and mating activity peaked in July and August, with a copulating pair observed in September.
- Mist netting revealed species-specific activity patterns and a strong male bias in E. nilssonii.

## Abstract

Bats play a vital role in ecosystems and can serve as early indicators of environmental change. However, their use of high-altitude habitats during the active season remains poorly understood. In this study, we investigated the summer and autumn activity of the northern bat (Eptesicus nilssonii) and other species at Lodowa Cave in the Tatra Mountains, southern Poland. To identify the species and study their presence, bats were captured using mist nets near the cave entrance. During the study, 723 bats representing 10 species were captured between June and November. The northern bat was the most abundant throughout the entire season. Several other species, including Myotis and Plecotus, also regularly used the site for swarming. Activity peaked in mid-summer, and species showed different nightly activity patterns. Our results demonstrate that high-altitude ice caves are crucial swarming and mating sites for cold-adapted E. nilssonii. These findings highlight the importance of protecting such unique mountain habitats in a warming climate.

The aim of this study was to examine the role of a high-elevation ice cave (Lodowa Cave in Ciemniak, Mt. Ciemniak, 1715 m a.s.l., Tatra Mountains, Poland) in the seasonal and nightly activity of bats. Bat activity was monitored using mist-netting and direct observations during the summer and autumn seasons of 2008–2011 and 2021. A total of 723 bats representing 10 of the 28 species known from Poland were captured. Eptesicus nilssonii predominated (57.5% of the total) and exhibited consistently high activity throughout the study period. Males predominated in almost all species, with E. nilssonii showing a strong male bias (85%), while adults were dominant and juveniles were rare (only 1.2% in E. nilssonii). Species composition and abundance varied seasonally, and swarming activity occurred between June and November, with a clear peak in July and August. Activity patterns were species-specific: E. nilssonii showed a pronounced peak approximately two hours after sunset, while M. mystacinus and P. auritus displayed distinct temporal activity profiles. A copulating pair of E. nilssonii was recorded in September 2011. Our findings suggest that high-altitude ice caves serve as key summer and autumn swarming and mating sites for E. nilssonii, highlighting their ecological importance in a warming climate.