Cowie R.J. & Hinsley S.A. (1987) Breeding success of Blue Tits and Great Tits in suburban gardens. ARDEA 75 (1): 81-90

Great Tits and Blue Tits, breeding in suburban gardens, were studied in areas of North Cardiff from 1981 to 1983. The two areas differed in the density and species of tree present, there being a higher density of mature native trees in Cyncoed than Heath. The density of Blue Tits breeding in Cyncoed was 13.7 pairs/10 ha similar to densities recorded in deciduous woodland. The density of Great Tits in both areas was low, and Blue Tits were approximately three times as numerous. Both species suffered a reduction in breeding success, rearing approximately half as many young as comparable populations breeding in deciduous oak woodland. Most of the reduction was due to nestling mortality from starvation. Great Tits in gardens began breeding earlier than those in woodland, but the Blue Tits did not. In 1981 and 1982 Blue Tit breeding success declined throughout the breeding season. In 1983 there was no such relationship. High rainfall around the time of peak hatching in Cyncoed is thought to explain the poor breeding success in this area during 1983. In 1981, when Blue Tits began breeding earlier than in subsequent years, there was a relationship between breeding success and the density of trees within 25 m of the nest. The two species which came into leaf first, Rowan and Oak, made the most significant contribution to this relationship. An analysis was performed to examine intra- and interspecific interference in nestbox selection. There was evidence of interference between Blue Tits at distances of 40-50 m, but no evidence of interference in Great Tits or between the two species. The reduction in breeding success in suburban gardens was similar to that recorded by other workers in suburban parks and cemeteries. The adaptations of both species to suburban habitats are discussed.