Indications of recent changes in status in the British Isles of the frog (Rana temporaraia) and the toad (Bufo bufo)

Abstract

Two surveys are described which were designed to provide information on changes in status in the British Isles of the frog (Rana temporaria L.) and the toad (Bufo bufo L.). Questionnaires were distributed asking for information and conclusions are based on replies referring to 1079 localities and 314 individual breeding sites. Replies indicated that the frog decreased slightly over most of the British Isles during the 1940s and 1950s, and suffered considerable declines over most of England throughout the 1960s. Moderate declines occurred in Scotland and Northern Ireland during the last half of the decade. Declines for the toad probably followed a similar pattern.The garden pond was the only habitat in which either species increased. Both the frog and the toad decreased markedly in breeding sites on agricultural land in the early 1960s, but during the late 1960s declines were less severe.The main reason for the declines has probably been loss of suitable wetland habitat due to sites being filled in, drained or physically modified in some way. Insecticides are only likely to have been harmful in sites where unusually high pollutant concentrations occurred. Other possible contributory factors are discussed and of these road mortality is perhaps the most important. Recent declines for the frog were significantly related to human population density.