Reduce pesticide, herbicide or fertiliser use
Overall effectiveness category Likely to be beneficial
Number of studies: 2
Background information and definitions
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 reducing pesticide, herbicide or fertiliser use 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 six hours from sunset on two nights. Surveys were repeated every 50 days from March 2004 to June 2005.Study and other actions tested
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 significantly 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 reference 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.Study and other actions tested