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 continuous and fragmented woodland habitats to determine the effect of fragmentation on behaviour, breeding success and turnover.

2. Information on home range and territorial behaviour was obtained from 23 radio-tagged individuals. Eight of these were in one large wood (continuous) and the rest in an area containing < 0.5% woodland (fragmented). Measures of breeding success and turnover were assessed in up to 67 territories in woods ranging from 0.1 ha to 196 ha.

3. Owls occurred in all woods > 4 ha and in up to 45% of wood < 4 ha.

4. Home range size was inversely related to wood size. For male owls, wood isolation and wood size accounted for 80% of the variation in horne range size.

5. In the fragmented woodland area tawny owl home ranges contained more woodland than expected from random. Within horne ranges, usage of habitat was such that woodland > buildings > grassland > arable areas. Owls utilized the grassland and arable areas by hunting from the ground.

6. In continuous woodland owl horne ranges overlapped more and they were more often involved in territorial behaviour than those in fragmented woodland.

7. There was a negative relationship between small mammal abundance and wood size.

8. For all years combined there was a quadratic relationship between wood size and breeding success, suggesting that owls perform better in intermediate-sized woods.

9. Turnover was highest in the smallest woods and lowest in the intermediate woods.

10. It is concluded that the intermediate woods, where food is abundant and energetic costs are not great, present an optimum habitat for tawny owls in this area.

11. The study indicates that data on breeding success and turnover are essential in determining the effects of habitat fragmentation and that these effects may not be easy to predict, given information from non-fragmented areas.