Factors affecting predation by buzzards Buteo buteo on released pheasants Phasianus colchicus

1. Information on the effects of wildlife predation on game and livestock i s required to allow improved management of all organisms involved. Monitori ng of prey, predators and predation mechanisms each suggests important meth ods, illustrated here by data from common buzzards Buteo buteo and ring-nec ked pheasants Phasianus colchicus. 2. Location data from 136 radio-tagged common buzzards, together with prey remains from 40 nest areas, records from 10 gamekeepers and vegetation surv eys, were used to investigate raptor predation at 28 pens from which pheasa nts were released in southern England. 3. Among 20 725 juvenile pheasants released in 1994-95, gamekeepers attribu ted 4.3% of deaths to buzzards, 0.7% to owls, 0.6% to sparrowhawks, 3.2% to foxes and 0.5% to other mammals. 4. Fresh pheasant remains were found on 7% of 91 visits to buzzard nests, a nd 8% of radio-tagged buzzards had significantly more association than othe r buzzards with pheasant pens. 5. Predation by buzzards was most likely to be recorded at release pens wit h little shrub cover, deciduous canopies and a large number of released phe asants. The number of pheasants killed was greatest in large pens with exte nsive ground cover, and the highest proportion of released pheasants was ki lled in large pens where few were released. However, only 21% of 55 release s had > 2 pheasant kills per week. 6. Radio-tagged buzzards were located most often at pheasant-release pens w ith open, deciduous canopies. Pens were most likely to be visited by buzzar ds that had fledged nearby, but the proximity of buzzard nests had little i nfluence on how much predation occurred. 7. Only a minority of buzzards associated frequently with pheasant pens, an d predation was heavy at only a minority of sites, where pen characteristic s and release factors probably made it easy for individual buzzards to kill pheasants. We suggest that the occasional heavy losses could be avoided by encouraging shrubs rather than ground cover in pens, by siting pens where there are few perches for buzzards, and perhaps also by high-density releas es.