Sm. Redpath, HABITAT FRAGMENTATION AND THE INDIVIDUAL - TAWNY OWLS STRIX ALUCO IN WOODLAND PATCHES, Journal of Animal Ecology, 64(5), 1995, pp. 652-661
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.