L. A. Batten

Population Dynamics of Suburban Blackbirds

During this century the Blackbird has become one of the commonest urban and suburban song-birds in Britain. In an effort to discover why town life attracts so many Blackbirds, the author has looked closely at the B.T.O. data, derived mainly from ringing and nest records, and has found interesting differences in productivity between London and rural populations.

Bird Population Changes for the Years 1973–74

The population trends apparent in the last few years continue, with further increases in many of our small resident birds. In contrast, several of the summer visitors remain at a very low level while some, such as the Swallow, have suffered further marked decreases.

Bird Population Changes for the Years 1975–76

The year 1976 saw decreases in many resident birds, particularly the smaller species. Both partridges made substantial increases and the Whitethroat continued to recover from the 1969 population crash, but has a long way to go yet.

Bird Population Changes for the Years 1974–75

Many resident birds are now maintaining higher population levels than was the case during the first ten years of the CBC, but some summer visitors are much less common. However, the decline in Redstart and Sedge Warbler seems to have halted.

The Seasonal Distribution of Recoveries and Causes of Blackbird Mortality

An analysis of ringing recoveries for Blackbirds since 1909 has shown a change in their seasonal distribution, fewer birds being found dead in winter. Proportionally more birds are now killed by traffic and cats in the breeding season. June-July is a critical period for juvenile Blackbirds, particularly if these months are relatively dry.

Bird Population Changes for the Years 1971–72

Notable increases in the population levels of Wren, Goldcrest and Redpoll were recorded by the Common Birds Census in 1971–72; however, Corn Bunting and Jackdaw showed a decline. Among summer visitors several West African wintering birds remain at a much reduced level.

Bird Population Changes for the Years 1972–73

The Wren and other small resident birds continue to increase, and the Goldcrest is now ten times commoner than it was a decade ago. Some summer visitors, however, have now reached their lowest ‘index’ since the Common Birds Census began.