Relative importance of avian groups in the diets of British and Irish predators

t is frequently of interest to have some idea 1. of the level of predation being suffered by bird species.However, the field experiments required to estimate such figures are difficult and time-consuming and could be unethical.The purpose of this study is to summarise available data on what proportion of British and Irish predators' diets consist of different bird groups and to give an estimate of daily food requirements.In future work, where appropriate experiments are impractical, the data should allow a rough estimate of likely predation rates, based on a knowledge of predator population density in individual circumstamces.Data were culled from the literature on the diets of British and Irish predatory mammals and birds.For each predator species, an attempt was made to find two or more studies on the diet where the number of food items reported was at least about 30.Studies were only included if they were carried out in the British Isles; urban data were omitted.In each case, an estimate was made of the percentage of the mass of the predator's diet that consisted of birds or their eggs.Where sufficient data existed, the contribution of different bird groups to the total was also assessed.In cases where estimating mass was not possible, the contribution of birds to the diet was estimated as the proportion of total food items recorded.This technique was checked and found to be accurate by calculating both the mass and the proportion of individual items for a number of studies where this was possible and comparing the two.