Pollutants endanger native bats

bats

The population of bat colonies in Europe has been steadily declining for decades. A new study on the lesser horseshoe bat shows that this is due not only to a reduction in the food supply and habitat, but also to increased exposure to pollutants. Accordingly, lead and cadmium in particular, but also organic environmental toxins, endanger the continued existence of native bats.

Flocks of bats once inhabited fields, caves and settlements in Europe, but in the second half of the 20th century their numbers began to decline steadily. The numbers of the only flying mammal have declined so much that where once a hundred bats lived, there is now only one. One reason for this is the sharp decline in insects, which are the main food source for bats. But the animals are also increasingly threatened by a restriction of their habitat. On the one hand, the artificial lights at night disturb the natural day-night rhythm of the nocturnal animals. On the other hand, building renovations deprive the animals of the niches and loopholes they need to be able to move into summer or winter quarters.

Pollution in sight

But there is another factor responsible for declining bat populations: exposure to pollutants. A current study on the populations of the Lesser Horseshoe Bat (Rhinolophus hipposideros) in the Bavarian-Tyrolean Alps region under the direction of Birgit Schlick-Steiner from the University of Innsbruck shows how serious these are for the continued existence of the animals. One of the smallest bat species native to Europe, the lesser horseshoe bat is the size of a thumb and lives for up to three decades. Their populations also decreased extremely between 1950 and 1980.

To find out why, the researchers examined the concentration of lead and cadmium in the faeces of the animals. Both are inorganic heavy metals that can have toxic effects on the metabolism even in small concentrations. The result: both lead and cadmium were present in significantly increased concentrations. According to the researchers, there is a connection between the extinction of lesser horseshoe bat colonies and the increased lead levels. “The heavy metals cause coordination problems in bats, which can reduce hunting success or even lead to the inability to fly,” explains Birgit Schlick-Steiner.

Fuels, paints and other anthropogenic sources

The pollutants probably come from fuels, but at least in part also from industry and some paints and contaminants from artificial fertilizers in agriculture. In addition to the heavy metals, scientists have also discovered organic pollutants based on carbon bonds in potentially dangerous amounts. These are difficult to break down, are stored in the fat reserves of the animals and thus reduce their reproductive success.

In order to be able to conserve the native bat colonies in the long term, Schlick-Steiner and her colleagues advocate a greater reduction in pollution in the environment. “We should avoid using highly toxic wood preservatives and under no circumstances use up old stock,” warns Schlick Steiner. “Products containing heavy metals, such as some industrially produced fertilizers and paints, should also no longer be used.” In addition, treated waste wood should no longer be used as firewood, but should be disposed of properly in order to prevent the release of heavy metals that are harmful to animals – but also to people.

Lesser horseshoe bats are finding less and less habitat

The study also confirmed that the lesser horseshoe bats are also endangered by other factors in their population. Schlick-Steiner and her team found that the habitats of the lesser horseshoe bat were being significantly restricted due to a decline in deciduous forests. Schlick-Steiner thinks that the lack of retreats for bats should be stopped primarily by rethinking the construction method: “Particularly in rural areas, freely accessible, unlit entry and exit options should be created in roof structures and the proportion of deciduous trees in forests are raised to allow bats to resettleā€.

Source: University of Innsbruck

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