Factors affecting the numbers and breeding success of Stone Curlews Burhinus oedicnemus at Porton Down, Wiltshire

Abstract

The numbers and breeding success of the Stone Curlew Burhinus oedicnemus, a rare bird in the UK, were studied on chalk downland at Porton Down, Wiltshire, from 1987 to 1996. The number of pairs varied annually between nine and 19 and was positively correlated with spring counts of Rabbits in the current and previous years. This correlation probably results from a previously documented preference for very short vegetation strewn with small stones created by grazing and soil disturbance by Rabbits. The average number of young fledged per pair was adequate to maintain a stable population, but varied by an order of magnitude among years. Annual variation in chick survival had the largest influence on variation in overall productivity, because breeding failures at the egg stage were usually replaced. Differences in chick survival among years were not correlated with the mean rate of growth of chicks. Nest success and overall breeding success were positively correlated with a spring Rabbit count and, for nest success, there was also a negative effect of the number of Foxes culled per unit effort, which may be an index of Fox numbers. The effect of Rabbit abundance might occur because predators only seek out Stone Curlew eggs and chicks when Rabbits are scarce. It is recommended that the high Rabbit population is maintained as this appears to be beneficial to Stone Curlews breeding on seminatural grassland.