Evidence for the indirect effects of pesticides on farmland birds

Abstract

Indirect effects of pesticides, operating through the food chain, have been proposed as a possible causal factor in the decline of farmland bird species. To demonstrate such a link, evidence is needed of (1) an effect of food abundance on breeding performance or survival; (2) an effect of breeding performance or survival on population change; and (3) pesticide effects on food resources, sufficient to reduce breeding performance or survival, and hence to affect the rate of population change. Evidence under all three categories is only available for one species, the Grey Partridge Perdix perdix , although data showing effects of pesticides on food resources and relationships between food resources and breeding performance are also available for some other species. This paper reports on recent work investigating the effects of pesticides on Yellowhammer Emberiza citrinella and Skylark Alauda arvensis during the breeding season. The probability of brood reduction in Yellowhammer was affected by the proportion of the foraging area around the nest which was sprayed with insecticide. No significant effects of pesticides were recorded on Skylark chick condition or growth rate, but sample sizes were small. Invertebrate food abundance affected chick condition (Skylark) and the number of chicks fledging (Yellowhammer and Corn Bunting Miliaria calandra ; relationship for the latter derived from re-analysis of data from an earlier study). Other recent work is briefly reviewed and the current evidence for the indirect effects of pesticides is summarized. Significant knowledge gaps are identified and some of the issues involved in resolving these are discussed.

Effects of breeding habitat and field margins on the reproductive performance of Skylarks (Alauda arvensis) on intensive farmland

“…Yet, the relationship between food availability and nestling condition or survival is not consistently positive, perhaps because factors like accessibility, prey profitability and nutrient composition are not always accounted for. Although some studies found improved nestling weight and survival when food availability around the nest was higher, for example for Yellowhammer Emberiza citrinella (Hart et al 2006), Linnet Carduelis cannabina (Bradbury et al 2003) and Corn Bunting Miliaria calandra (Brickle et al 2000;Boatman et al 2004), other studies could not detect such correlations for Chaffinch Fringilla coelebs (Bradbury et al 2003), Yellowhammer (Bradbury et al 2003) and Yellow Wagtail Motacilla flava (Gilroy et al 2009). For Skylarks, there are indications that nestling condition is significantly affected by the abundance of chick food within 100 m of the nest (Boatman et al 2004).…”

Contrasting bird communities along production gradients of crops and livestock in French farmlands

“…neighboring grasslands and hedgerows (Girard et al, 2012). Negative impacts of pesticides on insectivore bird populations have also been previously observed (Boatman et al, 2004;Hallmann et al, 2014).…”

“…Intensive management of cropland, such as insecticide use (Boatman et al, 2004) and removal or degradation of field margins (Wilson et al, 1999), has previously been found to reduce invertebrate abundance. The decline of invertebrate food for birds in intensive cropland has been observed repeatedly (Wilson et al, 1999) and requires birds to forage in Table 1 Relative importance of predictor variables with regards to each bird community descriptor.…”

Scientific Opinion addressing the state of the science on risk assessment of plant protection products for non‐target arthropods

“…The mortality among NTAs after application of such PPPs often approached 100 % a few days after the spray, and substantial effects lasted for up to two months. Boatman et al (2004) combined data available from published literature with their own experiments and concluded that 'indirect effects of pesticides indeed do occur, although, apart from the Grey Partridge, unequivocal evidence is only available for effects of insecticides. There is, however, strong circumstantial evidence for effects of herbicides, from a variety of sources; unfortunately practical difficulties in demonstrating indirect effects arising from herbicides have prevented their confirmation so far.…”