Winter cave trips endanger wintering bats

Bats spend almost half a year hibernating, thus avoiding the harshness of the winter. For the winter, bats hide in underground spaces – in Estonia, they favour basements, mines, caves, old military tunnels and shelters. The main criterion for the choice of wintering grounds is the temperature, which must not fall below zero; high humidity is also a plus. Wintering bats are not well suited to situations where they are unduly disturbed. There are scattered farm cellars and other smaller places for wintering all across Estonia. They can offer a wintering ground to a few or up to twenty individuals. It is quite a different tale with large wintering places, where hundreds or thousands of individuals congregate during the cold season. About a dozen such places are known throughout Estonia.

Bats prepare thoroughly for the winter. Preparations begin as early as in August, when the young animals are independent and no longer need care. Bats then diligently gain weight, catching prey in habitats where insects are particularly abundant at that time. This increases the adipose tissue that is necessary for surviving the winter without eating. Most of the collected energy is used for periodically waking from their slumber during the winter. Wintering is therefore very costly in terms of energy use.

Humans also want to visit the caves. Cave tourism and underground adventure trips are most popular from autumn to spring. On the other hand, all larger Estonian caves (or rather artificial caves) are important wintering grounds for bats. That is why most of these caves and tunnels are subject to nature conservation. It is forbidden to visit most bat wintering grounds from 1 September to 30 April. There are also caves where the ban on visiting applies all year (such as the Piusa cave system). The ban on visiting caves during winter is due to the fact that moving around in the caves and the accompanying noise and light wake bats from their hibernation. This happens regardless of whether people notice the animals or disturb them on purpose.

As bats consume most of the energy stored in the autumn while waking up during the winter, the disturbance caused by adventurers and tourist groups exploring the caves during their hibernation may cause the bats to run out of energy before spring and die or be too weak to cope after waking from the hibernation.

Do not visit caves in the winter! The impact of humans visiting the wintering grounds of bats can end up being rather extensive. The impact is particularly great in low and small caves. If people visit higher and larger caves, the light and sound that carries to the animals is weaker and, therefore, their impact is less severe. For the bats to fare well in the future and enjoy a peaceful and energy-saving hibernation, we should not visit caves in the winter!

Full article in the December 2019 issue of Eesti Loodus, pages 60–62. http://www.eestiloodus.ee/arhiiv/Eesti_Loodus12_2019.pdf

                                                                                                                      Authors: Rauno Kalda, Oliver Kalda

                                                                                                                    Editor: Reigo Roasto