Indirect effects of pesticides on breeding yellowhammer (Emberiza citrinella)

Intensification of agriculture is believed to have caused declines in farmland bird populations. One of the key elements of recent agricultural intensification is the increased use of pesticides. However, studies elucidating relationships between individual management practices and responses in bird populations remain rare. Here, evidence is presented of indirect effects of pesticides on behaviour and nestling condition of yellowhammers (Emberiza citrinella L.). Insecticide use was associated with reduced abundance of invertebrate food at the field scale resulting, early in the season (when nestlings were fed exclusively on invertebrates), in a negative correlation with yellowhammer foraging intensity. There was also a negative relationship between insecticide use and nestling body condition. While cumulative effects of repeated spraying can have impacts, the occurrence of any insecticide spraying in the breeding season may be more detrimental than multiple sprays at other times. Minimising applications of persistent broad-spectrum insecticides during March-June, the provision of alternative unsprayed foraging habitat and advice on mitigating indirect effects of pesticides to advisers and users are likely to benefit nesting yellowhammers.