The relationship between the numbers of hibernating brown long-eared bats (Plecotus auritus) and weather conditions (ambient temperatures and precipitation)

Abstract: This study investigates the relationship between outdoor temperatures, periods of prolonged precipitation and the numbers of brown long-eared bats (Plecotus auritus) in hibernacula during the annual bat census. It draws on census data from three complexes: in the Amsterdamse Waterleidingduinen, the Kop van Schouwen and Klein Heidekamp, in which an average of more than ten bats were present per winter over a period of 25 years. The weather indices were examined at nine points in time prior to the day of the census (42, 35, 28, 21, 14, 7, 5, 3 and 1 day respectively). KNMI weather observations from nearby weather stations were used to calculate the mean temperature (x̅TG), the number of (adjusted) frost days (nTN) and the sum of the negative minimum temperatures (ƩTN). In addition, the duration (ƩDR) and volume of precipitation (ƩRH) were summed for the nine periods. Pearson correlation tests were used to calculate the degree of correlation between the numbers of bats in each hibernaculum and these weather indices. It was found that more frosty days and a high cold count between 42 and 21 days prior to the count were associated with higher numbers of long-eared bats in hibernacula. Conversely, during the same periods, a negative association was found between mean outdoor temperatures and numbers of long-eared bats. No significant correlation was found between the precipitation indices and the numbers of longeared bats in any of the hibernacula for any period prior to the census day. In conclusion, the article discusses the possible significance of some ecological adaptations by the long-eared bat to cold conditions.