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Providing evidence to improve practice

Action: Reduce pesticide or herbicide use generally Bird Conservation

Key messages

Read our guidance on Key messages before continuing

  • A single small study from the UK investigated population level effects of reduced chemical inputs, and found that the populations of some species increased when pesticide use was restricted alongside other interventions.
  • Three studies, two replicated, one controlled, from the UK found that some or all species were found at higher densities on sites with reduced pesticide inputs, in one case with other interventions as well. Five studies from the UK, four replicated, four controlled, found that some or all species were not found at higher densities on fields or sites with reduced chemical inputs, or were not associated with reduced inputs.
  • A controlled before-and-after study from the UK found that grey partridge Perdix perdix chicks had higher survival on sites with reduced pesticide applications. A replicated study from the UK found that reduced chemical inputs had a negative relationship with partridge brood size and no relationship with survival or the ratio of young to old birds.

 

Supporting evidence from individual studies

1 

A controlled before-and-after study in 1989-94 in a 28 km2 area of arable farmland in Sussex, England (Aebischer & Potts 1998), found significantly higher survival rates of grey partridge Perdix perdix chicks on 21 km2 with irregular insecticide applications, compared to a 7 km2 farm with insecticide applications four times a year (average of 34% survival on low application farms vs. 22% on high application farm). Before the start of intensive insecticide application (1970-88), there was no difference between areas (27% survival on low application farms vs. 30% on intensive application farm).

 

2 

A small replicated controlled study from May-June in 1992-8 in Leicestershire, England (Stoate 2002), found that the abundance of nationally declining songbirds and species of conservation concern significantly increased on a 3 km2 site where pesticide use was restricted (alongside several other interventions), although there was no overall difference in bird abundance, species richness or diversity between the experimental and three control sites. Numbers of nationally declining species rose by 102% (except for Eurasian skylark Alauda arvensis and yellowhammer Emberiza citrinella). Nationally stable species rose (insignificantly) by 47% (eight species increased, four decreased). The other interventions employed were: ‘Manage hedges to benefit wildlife’, ‘Plant wild bird seed cover strips’, ‘Provide supplementary food’, ‘Control predators’ and ‘Create beetle banks’.

 

3 

A replicated study in 1999 and 2003 on farms in East Anglia and the West Midlands, England (Stevens & Bradbury 2006), found that five of twelve farmland bird species analysed were positively associated with a general reduction in herbicide use and conservation headlands. This study is discussed in more detail in ‘Leave headlands in fields unsprayed (conservation headlands)’.

 

4 

A randomised, replicated, controlled trial on four farms in southwest England, in 2003-6 (DEFRA 2007), found that no more foraging birds were attracted to 12, 50 x 10 m plots of permanent pasture with no fertiliser impact, compared to 12 control (conventionally managed) plots. Experimental plots were managed in the same way as control plots except for the lack of fertiliser, and all plots were cut twice in May and July, and grazed in autumn/winter. This study is also discussed in ‘Reduce management intensity on permanent grassland’, ‘Undersow spring cereals’, ‘Raise mowing height on grasslands’, ‘Reduce grazing intensity on permanent grasslands’ and ‘Plant wild bird seed or cover mixture’ .

 

5 

A replicated trial in 2004-2006 in northwest England (Mortimer et al. 2007) found no differences in bird numbers between conventional and minimum input barley fields. Sixteen trial fields were sown with spring barley each on a separate dairy or mixed farm in Cheshire, Staffordshire and north Shropshire. One half of each barley field was managed conventionally, the other half managed with minimum pesticide inputs (no insecticide after 15 March, no broad-leaved herbicide after 31 March, limited graminicides). Birds were monitored on each field, in summer 2005 and winter 2005/06.

 

6 

A replicated site comparison on 186 overwinter stubble fields in Devon, England (Bradbury et al. 2008), found that cirl buntings Emberiza cirlus, foraged at significantly higher densities on stubble fields under a ‘Special Project’ agri-environment option, compared to stubbles under standard agri-environment schemes (approximately 0.45 birds/ha for 102 special project stubble fields vs. 0.05 birds/ha for 52 conventional wheat stubbles and 0.15 birds/ha for 32 conventional barley stubbles). The special project stubbles were also preferentially selected to some extent by four other species of songbird. The special project was designed to encourage cirl buntings and allowed the use of fungicides, growth regulators and specified herbicides to control grass weeds, but prohibited the use of insecticides and herbicides to control broad-leaved weeds.

 

7 

A controlled study in 2000-5 on 61 ha of farmland in Bedfordshire, England (Henderson et al. 2009), found that both winter and summer densities of most farmland bird species studied were higher on areas with no pesticide input, compared to areas with conventional levels of pesticides (higher summer densities with no pesticides for 10 of 14 species, although only Eurasian skylark Alauda arvensis, yellow wagtail Motacilla flava and linnet Carduelis cannabina showed a significant increase; all songbirds and 16 of 19 species recorded in winter were at higher densities on zero-fertiliser fields). Skylarks were also found in significantly higher numbers on areas with zero fertiliser inputs, but no other species were affected by fertiliser reduction. This study also investigated the impact of set-aside provision (see ‘Provide or maintain set-aside’) and spring sowing wheat (see ‘Sow crops in spring, not autumn’).

 

8 

A replicated site comparison study on 1,031 agricultural sites across England in 2004-8 (Ewald et al. 2010) found that grey partridge Perdix perdix brood size was negatively related to reduced chemical inputs, when combined with overwinter stubbles. However, this combination of interventions was positively associated with year-on-year changes in partridge density. There were no relationships with overwinter survival or the ratio of young to old birds. This study describes the effects of several other interventions, discussed in the relevant sections.

 

9 

A replicated, controlled study from April-July and November-February in 2004-6 on 16 livestock farms in the West Midlands, England (Peach et al. 2011), found that there were no differences in the usage of barley fields between fields sprayed with only a narrow-spectrum herbicide (amidosulfuron, at 25-40 g/ha) and those sprayed with both a narrow- and a broad-spectrum herbicide. Insect-eating songbirds and crows showed reduced use of broad-spectrum-sprayed fields in summer and late summer respectively, but all other groups used fields at equal rates. Barley fields on the farms were split, with half being used for each treatment. Narrow-spectrum herbicide was applied in April-May and broad-spectrum in July.

 

Referenced papers

Please cite as:

Williams, D.R., Child, M.F., Dicks, L.V., Ockendon, N., Pople, R.G., Showler, D.A., Walsh, J.C., zu Ermgassen, E.K.H.J. & Sutherland, W.J. (2018) Bird Conservation. Pages 95-244 in: W.J. Sutherland, L.V. Dicks, N. Ockendon, S.O. Petrovan & R.K. Smith (eds) What Works in Conservation 2018. Open Book Publishers, Cambridge, UK.