Action: Convert to organic farming
- Evidence on whether organic farming benefits bats is mixed. Four replicated, paired, site comparison studies on farms in the UK and Greece had inconsistent results.
- Two studies in the UK found higher bat abundance and activity on organic farms than conventional farms. One of the studies found more bat species on organic farms, and the other study did not find a difference between farm types.
- One study in the UK found no difference in bat abundance between fields in organic and conventional farms. A study on Zakynthos, Greece found that a single yearly application of insecticide chemicals did not affect bat activity over traditional olive groves.
Organic farming is an agricultural system that excludes the use of synthetic fertilizers and pesticides and relies on techniques such as crop rotation, compost and biological pest control. Organic standards are strictly regulated in many countries prohibiting the use of chemicals and providing recommendations for management to conserve biodiversity.
Supporting evidence from individual studies
A replicated, paired, site comparison study in summer 2000 and 2002 on 24 pairs of farms in southern England and Wales, UK (Wickramasinghe et al 2003) found bat activity to be significantly higher over water habitats on organic farms than on conventional farms (447 vs. 144 total bat passes respectively). Bat activity did not differ significantly between farm types over pasture, arable or woodland habitats. Sixteen bat species were detected on organic farms and 11 on conventional farms but the difference was not significant. The activity of Pipistrellus and Nyctalus spp. did not differ significantly between farm types. Myotis spp. were recorded more on organic farms, and Rhinolophus spp. were only detected on organic farms with the majority in woodland habitats. Certified organic farms that had been established for 1–2 years were paired with nearby conventional farms of a comparable business, size, and number and area of habitat types. Two farms of each pair were sampled from June to September on consecutive nights. Selected habitats (pasture, arable land, water and woodland) found to be present on both farms of a pair were sampled. No details are given about the type or origin of water habitats sampled. Bat activity was recorded using bat detectors for 10 minutes at three random points within each habitat at each site. Recordings were taken for an hour and a half from one hour after sunset. Analysis of habitat surveys showed that pairs of farms were comparable in all aspects except for hedgerow height, which was significantly higher on organic farms.
In a replicated, paired, site comparison study in summer 2002 and 2003 on 65 pairs of farms in England, UK (Fuller et al 2005) significantly more bat passes were recorded on organic farms than non-organic farms (abundance index 6–75% higher). Significantly more species were also recorded on organic farms (species density 8–65% higher). Organic farms of at least 30 ha of arable land were paired with nearby non-organic farms matched by crop type and cropping season. Bat surveys using bat detectors were conducted along 3 km triangular transects starting in a randomly chosen field on each farm between June and August on both years. Habitat data collected at all sites showed that organic farms had a higher density of hedgerows, a greater proportion of grassland than cropped cover, smaller fields and wider and taller hedgerows with fewer gaps than non-organic farms. The study looked at a variety of taxa and details about the levels of bat activity and bat species recorded are not given.
A replicated, paired, site comparison study in summer 2005 in olive Olea europea groves on Zakynthos island, Greece (Davy et al 2007) found that bat activity did not differ significantly between six organic and six non-organic olive groves (average 0.8 vs. 1.1 bat passes/min respectively). Bat foraging activity and the activity of insect prey also did not differ significantly. Olive groves were similar in size, age, density of trees and altitude. Organic olive groves used organic pest control and no chemicals. Non-organic groves were treated with a yearly insecticide spray treatment. Bat and insect activity in both olive groves also did not differ significantly from that in six native woodland patches (oak and pine). Each site was sampled for three nights, with rotations between sites and habitat types. Bats were captured in mist nets and activity was recorded for an hour and a half from dusk in ten minute intervals rotating between four points within each site. Eleven bat species were detected.
A replicated, paired, site comparison study in summer 2003 on eight paired farms near Bristol, UK (Pocock & Jennings 2008) did not find a significant difference in the abundance of common pipistrelles Pipistrellus pipistrellus between organic cereal fields and nearby conventionally farmed fields (total 96 vs. 152 bat passes respectively). Pairs of fields were matched to control for habitat variables and were sampled simultaneously. Each site was sampled on one night between May and August. Bat activity was recorded from 45 minutes after sunset using bat detectors for 20 minutes at four different points along a transect at each site. Two sample points were located 50 m into the field, and two within 1 m from the field boundary.
- Wickramasinghe L.P., Harris S., Jones G. & Vaughan N. (2003) Bat activity and species richness on organic and conventional farms: impact of agricultural intensification. Journal of Applied Ecology, 40, 984-993
- Fuller R.J., Norton L.R., Feber R.E., Johnson P.J., Chamberlain D.E., Joys A.C., Mathews F., Stuart R.C., Townsend M.C., Manley W.J., Wolfe M.S., Macdonald D.W. & Firbank L.G. (2005) Benefits of organic farming to biodiversity vary among taxa. Biology letters, 1, 431-434
- Davy C.M., Russo D. & Fenton M.B. (2007) Use of native woodlands and traditional olive groves by foraging bats on a Mediterranean island: consequences for conservation. Journal of Zoology, 273, 397-405
- Pocock M.J.O. & Jennings N. (2008) Testing biotic indicator taxa: the sensitivity of insectivorous mammals and their prey to the intensification of lowland agriculture. Journal of Applied Ecology, 45, 151-160