The breeding biology of the Common Buzzard

摘要

In a long-term study of the Common Buzzard Buteo buteo in Avon, territorial pairs were counted every year (1982-2012) and full breeding performance was recorded for 20 years (1988-2007), the main study period. The population rose from 13 pairs in 1982 to 105 pairs in 2012 (from 19 to 92 pairs during the main study period). Breeding output (from all pairs) declined from 1.89 to 0.56 chicks/pair but varied quite widely between years. Nearest neighbour distance and territory size also declined. A density-dependent effect on reproduction was clearly shown, while rainfall in May depressed productivity significantly. Territory size did not correlate with brood size but territories with more than 50% arable crops produced fewer chicks. Even though output declined as density increased, the number of chicks fledged per unit area increased, implying that high breeding density is better for the population overall but not for individual pairs. The study population was probably self-supporting throughout and latterly it appeared to produce more adults than it could absorb. Other studies are discussed with a view to determining the reasons behind the extraordinary increase in the national population of Common Buzzards. It is suggested that this increase, which started in the late 1970s, was partly attributable to legislation introduced about 15 years earlier for the protection of birds and a generally positive attitude towards raptors.