Action: Reduce pesticide, herbicide or fertiliser use
Key messagesRead our guidance on Key messages before continuing
- Three studies evaluated the effects of reducing pesticide, herbicide and fertiliser use on bat populations. One study was in Mexico, one was in Portugal, and one in Germany.
COMMUNITY RESPONSE (3 STUDIES)
- Community composition (1 study): One replicated, site comparison study in Portugal found that farms using few or no chemicals had different compositions of bat species to farms using high chemical inputs.
- Richness/diversity (2 studies): One site comparison study in Mexico found that coffee agroforestry plantations using few or no chemicals had a higher diversity of insect-eating bat species than plantations with high chemical inputs, but the diversity of fruit and nectar-eating bat species did not differ. One paired sites study in Germany recorded more bat species over grassland with moderate or no fertiliser applications than grassland with high fertiliser applications.
POPULATION RESPONSE (2 STUDIES)
- Abundance (2 studies): Two site comparison or paired sites studies (one replicated) in Portugal and Germany found that farms or grasslands with few or no chemical inputs had higher overall bat activity (relative abundance) than those using high chemical inputs.
BEHAVIOUR (0 STUDIES)
Pesticides, herbicides and fertilisers may degrade bat foraging habitats and reduce the availability of prey. Bats may also become directly contaminated, as these substances can persist and accumulate in ecosystems. Exposure to contaminants may not only kill bats but can have serious sub-lethal effects. For example, pesticide exposure can cause altered behaviour, reproductive failure, and disruption of hormones and the immune system (Bayat et al. 2014).
For studies that involve excluding the use of pesticide, herbicide or fertiliser alongside other interventions, see ‘Threat: Agriculture – All farming systems – Use organic farming instead of conventional farming’.
Bayat S., Geiser F., Kristiansen P. & Wilson S.C. (2014) Organic contaminants in bats: trends and new issues. Environment International, 63, 40–52.
Supporting evidence from individual studies
A site comparison study in 2004–2005 in five agroforestry plantations and one montane rainforest in southeastern Chiapas, Mexico (Estrada et al. 2006) found that coffee agroforestry plantations using few or no chemicals had a higher diversity of insect-eating bat species than coffee agroforestry plantations with high chemical inputs, but the diversity of fruit and nectar-eating bat species did not differ. A higher diversity of insect-eating bat species was captured in plantations with low chemical use than in plantations with high chemical inputs (data reported as diversity index). The number of fruit and nectar-eating bat species was similar in plantations with low and high chemical use. More bat species were recorded in native rainforest (37 species) than in any of the five coffee agroforestry plantations (23–26 species). One site of native rainforest was sampled, and five sites on coffee agroforestry plantations with different amounts of chemical use (either none, organic compost, or different combinations of Thiodan, herbicide and fertilizer). Plantations with the highest chemical input used all three chemical types. At each of six sites, bats were captured with six mist nets placed along a 150 m transect for 6 h from sunset on two nights. Surveys were repeated every 50 days from March 2004 to June 2005.
A replicated, site comparison study in 2010 of 36 Mediterranean olive farms in southwestern Portugal (Herrera et al. 2015) found that traditional farms using few or no chemicals had greater bat activity and different compositions of bat species than intensive farms using high chemical inputs, but they did not differ significantly from semi-intensive farms. Bat activity overall was higher in traditional farms (average 6 bat passes/night) than intensive farms (1 bat pass/night). Species composition also differed (data reported as Sørenson’s index). No significant differences in bat activity or species composition were found between traditional and semi-intensive farms (average 3 bat passes/night). At least eight bat species were recorded (see original paper for data for individual species). Thirty-six olive farms (13 traditional, 12 semi-intensive and 11 intensive) were surveyed. Traditional farms used few or no chemicals, semi-intensive farms used a moderate chemical input and intensive farms used high and frequent chemical inputs (dimethoate and deltamethrin). Tree density and the use of mechanical methods varied between farms. Three olive farms (one per management type) were simultaneously surveyed every night for one week between July and September 2010 with a bat detector deployed in the centre of each farm.
A site comparison study in 2012–2013 of three grassland sites in Brandenburg, Germany (Starik et al. 2018) found that grasslands with moderate or no fertiliser applications had higher overall bat activity and more bat species than a grassland with high amounts of fertiliser applied. Overall bat activity (of 11 bat species) and the number of bat species recorded were higher over grasslands with moderate (average 11 bat passes/hour, 7 bat species/night) or no fertiliser applications (17 bat passes/hour, 7 bat species/night) than high fertiliser applications (5 bat passes/hour, 5 bat species/night). One site (1 ha) was sampled in each of three grasslands treated with different amounts of nitrogen (N) fertiliser (high applications: 225 kg/ha; moderate: 100 kg/ha; none applied). The site with high fertiliser applications was harvested three times/year, and the site with moderate fertiliser application was grazed (1 cow/ha). Sites were located a similar distance to settlements, water bodies and other land use types. At each of three sites, two bat detectors recorded bat activity simultaneously over a total of 46 nights in May–October 2012 and April–October 2013.
- Estrada C.G., Damon A., Hernández C.S., Pinto L.S. & Núñez G.I. (2006) Bat diversity in montane rainforest and shaded coffee under different management regimes in southeastern Chiapas, Mexico. Biological Conservation, 132, 351-361
- Herrera J.M., Costa P., Medinas D., Marques J.T. & Mira A. (2015) Community composition and activity of insectivorous bats in Mediterranean olive farms. Animal Conservation, 18, 557-566
- Starik N., Göttert T., Heitlinger E. & Zeller U. (2018) Bat community responses to structural habitat complexity resulting from management practices within different land use types - a case study from north-eastern Germany. Acta Chiropterologica, 20, 387-405