Risk of imidacloprid-treated seeds for red-legged partridges Alectoris rufa

Resumen del trabajo presentado a la 9th Conference of the European Ornithologists' Union, celebrada en la University of East Anglia (UK) del 27 al 31 de agosto de 2013.The use of pesticide-coated seeds is a very widespread practice that could pose a risk on granivorous farmland birds. The neonicotinoid insecticide imidacloprid is the most used insecticide for seed coating, and constitutes the main risk of poisoning for wildlife species feeding on seeds. Since 2010, we have developed an assessment of the risk of coated seed ingestion on an important game species in Spain, the red-legged partridge Alectoris rufa. In order to characterize the direct effects of ingestion of imidacloprid-treated seeds, we conducted two experiments with different doses and exposure times and recorded survival, body condition, and physiological and reproductive effects. Partridges feeding exclusively on seeds treated with the recommended dose of imidacloprid in the first experiment carried out in spring (10 days of exposure) showed a loss of body weight, altered biochemical parameters, increased oxidative stress and reduced carotenoid-based coloration. In the second one performed in autumn, such exposure was lethal for all partridges (n=32) after 21 days (with the first casualty recorded the third day of exposure). Imidacloprid exposure also reduced the fertile eggs rate (55% vs. 85% in controls) and increased chick mortality at day 32 post-hatching (70% vs. 34.6% in controls). On the other hand, we have studied the risk of exposure through a feeding trial with four experimental groups (n=4 pairs/group): untreated seeds only, treated seeds only, treated and untreated seeds without shifting the position of feeders between days, and treated and untreated seeds shifting the position. Partridges offered both kinds of diet clearly rejected imidacloprid-treated seeds, although their consumption tended to increase when the location of the feeders was shifted (14.77±6.32 vs. 7.3±4.2 % of total consumption). In another feeding trial, we have seen lower food consumption when treated:untreated grain was offered ad libitum in an increasing number of feeders (1:1 to 8:8), which may respond to the refusal of food under an unpredictable scenario of toxic grain availability. When offered only treated seeds, average daily consumption was 7.77±1.72 g / partridge, which is about the half of the LD50. Actually, one of the partridges ate 18 g in the first day of experiment and was found dead the next day. In conclusion, although partridges reject imidacloprid when they have an easily accessible untreated alternative, they may feed on small amounts that can exert severe toxic effects. In order to minimize risks posed for imidacloprid-treated seeds on farmland birds, it is essential to preserve margins and patches with natural vegetation to provide a clean food source for animals. Furthermore, given the high toxicity of the insecticide for wild birds, it seems recommendable, if possible, to replace it by less toxic alternatives.Peer Reviewe