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Providing evidence to improve practice

Action: Provide or retain set-aside areas on farmland Terrestrial Mammal Conservation

Key messages

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  • Four studies evaluated the effects on mammals of providing or retaining set-aside areas on farmland. Three studies were in the UK and one was in Switzerland.



  • Abundance (3 studies): Three replicated studies (including two site comparison studies), in the UK and Switzerland, found that set-aside did not enhance small mammal numbers relative to cropland or to uncultivated field margins and farm woodland, or brown hare numbers relative to numbers on farms without set-aside areas.


  • Use (1 study): A before-and-after study in the UK found that use of uncut set-aside areas by wood mice increased after crop harvesting.

Supporting evidence from individual studies


A replicated, controlled study in 1995 of set-aside on two farms in Gloucestershire, UK (Tattersall et al. 1997) found that establishing one-year set-aside areas on cropland did not increase small mammal abundance. Trapping success was lower in set-aside (0.6% of traps activated) than in the adjoining unharvested cereal crop (13% of traps activated) and hedgerow (30% of traps activated). Long-tailed field mouse Apodemus sylvaticus was the only species caught in set-aside. Sampling at two sites on each farm covered a hedgerow, a 20-m-wide strip of set-aside with adjacent cereal crop on one side of the hedge and a block of either set-aside (two sites) or cereal crop (two sites) on the other side. Set-aside was sown with a mix of wheat Triticum aestivum and oilseed rape Brassica napus (three sites) or left to regenerate naturally (one site). Fifty Longworth live traps were operated at each site for five nights/month in June–August 1995.


A before-and-after study in 1996–1997 on an arable farm in Wiltshire, UK (Tattersall et al. 2001) found that use of uncut set-aside areas by wood mice Apodemus sylvaticus increased after crop harvesting. After crop harvesting, uncut set-aside was used more than expected by chance, as were hedgerows. Cut set-aside was used less than expected by chance (results shown as preference indices). Use of cropped areas declined to an average 13% of wood mouse ranges after harvesting, from 54% before harvesting. Across two arable fields, a 3-ha block of set-aside and 3 km of 20-m-wide set-aside field margins were sown (grass/clover mix) in October 1995. In August 1996 and 1997, twenty-four alternate 50 × 6-m patches of cut and uncut set-aside were created alongside a hedge. The remaining 14-m width of set-aside was cut. Thirty-four wood mice were radio-tracked over ≥3 nights in June–July and September–November of 1996 and 1997.


A replicated, site comparison study in 2003–2004 in Yorkshire, UK (Askew et al. 2007) found that set-aside had similar numbers of small mammals compared to uncultivated field margins and farm woodland. There was no significant difference in the annual average numbers of small mammals caught in set-aside (1.6–2.0), 2-m margins (2.9–4.4 individuals), 6-m margins (2.5–3.6) and farm woodland (2.4–2.8). In the first year, fewer common shrews Sorex arenaeus were caught in set-aside (0.6) or farm woodland (0.6) than in 2-m margins (1.4 individuals) and fewer wood mice Apodemus sylvaticus were caught in set-aside (0.5) than in 6-m margins (1.1) and farm woodland (1.4). No other species differences between treatments were found. Set-aside areas were fallow for ≥5 years, with ≥90% of the area cut annually. Field margins, sown with grass, were 2 m wide (cut every 2–3 years) or 6 m wide (cut every 1–3 years). Farm woodland comprised young trees (age not stated), fenced and with grass generally uncut. Twelve small mammal traps were set in each of 20 plots/treatment (1 m from the habitat boundary) for four days in November–December in each of 2003 and 2004.


A replicated, site comparison study in 1992–2008 on 58 lowland arable and grassland sites in Switzerland (Zellweger-Fischer et al. 2011) found that set-aside areas on farmland were not associated with higher brown hares Lepus europaeus densities. Set-aside areas were not associated with hare density in either predominantly arable or predominantly grassland areas (data presented as statistical models). Fifty-eight sites (40 mostly arable, 18 mostly grassland), of 71–1,950 ha extent (total area approximately 400 km2) were studied. Forty-three sites included areas managed under agri-environment funding. This entailed establishing set-aside areas (not mown or fertilized, usually sown with wildflower seeds and retained for 2–6 years), maintaining hedgerows (with adjacent herbaceous strips) and low intensity management of meadows. Set-aside covered 3.0% of arable sites and 4.6% of grassland sites. Vehicle-based spotlight surveys for hares were conducted twice in February–March. Ten sites were surveyed annually in 1992–2008 and 48 were, on average, surveyed biennially over that period.

Referenced papers

Please cite as:

Littlewood, N.A., Rocha, R., Smith, R.K., Martin, P.A., Lockhart, S.L., Schoonover, R.F., Wilman, E., Bladon, A.J., Sainsbury, K.A., Pimm S. and Sutherland, W.J. (2020) Terrestrial Mammal Conservation: Global Evidence for the Effects of Interventions for terrestrial mammals excluding bats and primates. Synopses of Conservation Evidence Series. University of Cambridge, Cambridge, UK.