The assessment of mortality resulting from the ingestion of spent lead shot by mallard wintering in South East England.

Abstract

Ingestion of lead pellets has long been recognised as a cause of waterfowl mortalities. This paper investigates the extent of the problem in part of the United Kingdom. The examination of the guts of 578 Mallard from south east England showed a decline in pellet ingestion rate through the season and the level of pellet ingestion and estimated resulting mortality in this population is lower than that found by other workers in the U.K. This is thought to be a result of different availability of shot caused by differences in shooting intensity, availability of grit and depth of surface water in the different sites of sample collection. A simple equation which can be used to calculate the lead poisoning mortality over the hunting season is described. This takes into account the increased vulnerability of poisoned birds, the turnover of poisoned birds in the population, seasonal variations in the level of pellet ingestion and the differential mortality caused by the ingestion of different numbers of shot. This method of estimating mortality is applied to data from other investigations of lead ingestion by Mallard to allow comparison between sites and comparison with estimates derived using the method of Bellrose (1959). It is suggested that results of lead poisoning studies in waterfowl in other countries are not generally applicable to the U.K., that the problem in this country is not so severe as once thought, and that the mortality resulting from lead poisoning in this population of Mallard is much less significant than that resulting from shooting itself.