Influence of Woodland Area on Breeding Success in Great Tits Parus major and Blue Tits Parus caeruleus

Abstract

Reproductive performance of Great Tits and Blue Tits breeding in highly fragmented woodland was investigated in relation to woodland area in a landscape dominated by intensive arable agriculture in eastern England. Breeding performance was recorded for five years (1993-1997) for tits breeding in nestboxes in up to 43 woods ranging in size from 0.1 to 157 ha. Trends in the components of breeding success with woodland area were investigated using a linear, mixed model including both fixed and random effects, and logistic regression analysis. In both Great Tits and Blue Tits, breeding performance declined with decreasing woodland area. For Blue Tits, the decline was accounted for by the timing of breeding which was later in smaller woods. Great Tits showed a similar trend in laying date with woodland area, but over and above this effect of timing on breeding success, they also reared lighter young in smaller woods. The variation in first egg date accounted for by woodland area was about 25% for Great Tits and 33% for Blue Tits. In some years, failure at the nestling stage was frequent for Great Tits (but not Blue Tits) in small woods, but was not recorded to the same extent in large woods. The results are discussed in the context of previous studies of tit breeding success in relation to individual bird quality, habitat quality and availability, and the consequences of habitat fragmentation.