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

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, Wiltsh ire, from 1987 to 1996. The number of pairs varied annually between nine an d 19 and was positively correlated with spring counts of Rabbits in the cur rent and previous years. This correlation probably results from a previousl y documented preference for very short vegetation strewn with small stones created by grazing and soil disturbance by Rabbits. The average number of y oung fledged per pair was adequate to main tain a stable population, but va ried by an order of magnitude among years. Annual variation in chick surviv al had the largest influence on variation in overall productivity because b reeding failures at the egg stage were usually replaced. Differences in chi ck survival among years were not correlated with the mean rate of growth of chicks. Nest success and overall breeding success were positively correlat ed with a spring Rabbit count and,for nest success, there was also a negati ve effect of the number of Foxes culled per unit effort, which may be an in dex of Fox numbers. The effect of Rabbit abundance might occur because pred ators only seek out Stone Curlew eggs and chicks when Rabbits are scarce. I t is recommended that the high Rabbit population is maintained as this appe ars to be beneficial to Stone Curlews breeding on seminatural grassland.