Bats in the agricultural landscape – direct and indirect effects of pesticides and management practice

Bats 3

Project description

Agricultural intensification has brought about large-scale changes to the landscape worldwide. Traditional, relatively extensive mixed farming systems have been replaced by intensive systems with homogenous and highly productive arable fields treated with agrochemicals. Both, the habitat change and toxicological effects of pesticides are perceived to be major causes of the decline in many European bat populations. Bats are considered to be susceptible to pesticides even though effects other than mortality have not been studied and very little research has been done about their occurrence in the agriculture landscape.

Like other insectivorous mammals and birds, bats may receive more pesticide residue in their diets through contaminated insects than do herbivores because of food-chain build-up. Moreover, the high metabolic rates of bats in connection with flight and associated with small size, demand greater rates of food intake than less active or larger mammals. Greater food intake increases the amounts of pesticide residues available for concentration in fat. Other than small insectivorous mammals like shrews, bats risk mobilization of residues of lipophilic pesticides because of fat depletion during hibernation. Large doses of lipophilic pesticides concentrated in milk may be transferred to the offspring during nursing. In addition, many modern pesticides are suspected endocrine compounds and may have effects on the fertility or sex determination.

We surveyed bat activity and the availability of nocturnal insects on different representative crops in southern Palatine with respect to the vicinity to forests and settlements (putative roost). In order to get comparable data sets we performed bat activity measurements and insect trapping throughout entire nights and simultaneously on 10 sampling sites of a study area. Each of the 7 study areas comprised 8 different agricultural sampling sites as well as one in a traditional cultivated pasture and a forest respectively. In summary, our results revealed firstly, high bat activity as well as high insect availability on some of the examined sites in vegetable fields and apple orchards which was comparable or even higher than the activity in the nearby forests and pastures. Secondly, only very low bat activity and insect availability was proved for all examined vineyards.

The revealed high bat activity in cultivations that requiring high pesticide input like vegetable growing and apple orchards demonstrate the necessity of a risk assessment of pesticides on bats. The database for the risk assessment for small mammals so far only includes data about pesticide residue on large insects and might therefore underestimates the risk towards the small sized bats. In apple orchards in Palatinate the lipophilic insecticide Insegar (Fenoxycarb), a potential endocrine compound, is currently applied up to three times during the lactation period of bats. We therefore measured the residues of Fenoxycarb during two applications on various insect groups (accordingly to the diet of the native bat guilds) and in parallel monitored bat activity in the orchard. High and exceptionally high residues have been measured for small flying insects and canopy dwelling insects, respectively. We currently try to estimate the acute and reproductive risk for the different bat guilds using the data set.

In parts of southern Palatine the landscape is dominated by vineyards, a habitat shown to be of low quality for bats because of the demonstrated low food availability. By surveying bat activity and food availably pair wise on several retention ponds and neighbouring vineyards we evaluate if the creations of artificial wetlands benefits bats. On average a 160 times higher bat activity and a 4 times higher amount of insects was measured on the retention ponds in comparison to the vineyards. In summary, the creation of artificial wetlands is a possibility to create important foraging habitats for bats in the agriculture landscape.


Related publications

  • Peter Stahlschmidt & Carsten A. Brühl (2012) Bats at risk? – Bat activity and residue analysis of food items following insecticide applications in an apple orchard. Environmental Toxicology and Chemistry 31(7), 1556-1563. DOI: 10.1002/etc.1834
  • Peter Stahlschmidt & Carsten A. Brühl (2012) Bats as bioindicator species – The need of a standardized method for acoustic bat activity surveys. Methods in Ecology and Evolution 3, 503-508. DOI: 10.1111/j.2041-210X.2012.00188.x.
  • Peter Stahlschmidt, Achim Pätzold, Lisa Ressl, Ralf Schulz & Carsten A. Brühl (2012) Constructed wetlands support bats in agricultural landscapes. Basic and Applied Ecology 13, 196–203.