TERRITORY QUALITY AND REPRODUCTIVE SUCCESS IN THE DARTFORD WARBLER SYLVIA-UNDATA IN DORSET, ENGLAND

The relationship between territory quality and reproductive success was investigated in a population of the Dartford warbler Sylvia undata, breeding at Holt Heath National Nature Reserve, Dorset, UK. Reproductive success, as measured by the number of young produced, was high, with most pairs raising two broods of young. Nine separate measurements of territory quality revealed considerable variation and larger territories contained more heather Calluna vulgaris, but not more gorse Ulex europaeus. There was no initial relationship between measures of territory quality and reproductive success, but when adult losses were removed from the analysis, territories containing more gorse produced more young. Territories containing more gorse were also closer to the road where most adult losses occurred, thus initially masking the positive relationship between the amount of gorse and reproductive success. The study suggests that the amount of gorse within a territory, and distance to a road, are the two most important territory quality variables affecting reproductive success in this population. These findings have important implications for the future conservation of Dartford warblers, and in particular for the effective management of nature reserves on the remaining lowland heaths of southern England.