Relationships between farming and hunting: effects of pesticide-coated seeds on red-legged partridges

Abstract

The use of agrochemicals is suspected to be a major cause of population declines of farmland birds from Western Europe. Apart from indirect effects like reduction of available food and optimal habitat, ingestion of pesticide-coated seeds constitute a potential way of direct intoxication. Although the most toxic chemicals are being legally restricted, some of the pesticides currently used for seed coating can cause adverse effects when consumed by birds. The use of coated seeds is a widespread practice, and cereal seeds consitute a major portion of partridge diet during autumn and winter, when alternative food sources are scarce. On the other hand, colour, taste or texture of the coat can make seeds unpalatable for birds, reducing the risk of ingestion. The aim of the present study is to assess the effects of coated seed ingestion by red-legged partridge (Alectoris rufa) on individual level and population viability. The first phase of the project consisted in the experimental exposure to five currently used chemicals, two insecticides (imidacloprid and natural pyrethrins) and three fungicides (difenoconazole, maneb and thiram). The second phase consists in the assessment of the environemntal exposure of partridges to coated seeds. We report deleterious effects of some of these chemicals on survival, mass and body condition, immune response and metabolism. Several reproductive parameters such as fecundation rate and chick immunocompetence and survival were affected by parental exposure to some of the tested pesticides. Difenoconazole and natural pyrethrins were the less toxic compounds within each kind of pesticide, so it would be recommendable to use them as alternatives to the most toxic compounds when possible. Experimental assessment of food choice revealed that, while some pesticides such as thiram had a repellent effect, the more toxic imidacloprid was not actively rejected by partriges, thus being potentially eaten by animals in the field. Balancing the risks and advatanges of seed coating is a necessary issue in which interests of farmers, hunters and conservationists meet. The information provided in this study will contribute to an appropriate management of this question.