HABITAT FRAGMENTATION AND THE INDIVIDUAL - TAWNY OWLS STRIX ALUCO IN WOODLAND PATCHES

1. The aim of this study was to examine tawny owls Strix aluco in cont inuous and fragmented woodland habitats to determine the effect of fra gmentation on behaviour, breeding success and turnover. 2. Information on home range and territorial behaviour was obtained from 23 radio-ta gged individuals. Eight of these were in one large wood (continuous) a nd the rest in an area containing < 0.5% woodland (fragmented). Measur es of breeding success and turnover were assessed in up to 67 territor ies in woods ranging from 0.1 ha to 196 ha. 3. Owls occurred in all wo ods > 4 ha and in up to 45% of wood < 4 ha. 4. Home range size was inv ersely related to wood size. For male owls, wood isolation and wood si ze accounted for 80% of the variation in horne range size. 5. In the f ragmented woodland area tawny owl home ranges contained more woodland than expected from random. Within horne ranges, usage of habitat was s uch that woodland > buildings > grassland > arable areas. Owls utilize d the grassland and arable areas by hunting from the ground. 6. In con tinuous woodland owl horne ranges overlapped more and they were more o ften involved in territorial behaviour than those in fragmented woodla nd. 7. There was a negative relationship between small mammal abundanc e and wood size. 8. For all years combined there was a quadratic relat ionship between wood size and breeding success, suggesting that owls p erform better in intermediate-sized woods. 9. Turnover was highest in the smallest woods and lowest in the intermediate woods. 10. It is con cluded that the intermediate woods, where food is abundant and energet ic costs are not great, present an optimum habitat for tawny owls in t his area. 11. The study indicates that data on breeding success and tu rnover are essential in determining the effects of habitat fragmentati on and that these effects may not be easy to predict, given informatio n from non-fragmented areas.