Once in a while, BTO survey results bring great cheer. The Peregrine Survey of 1991 is one such instance. The survey has revealed that the Peregrine Falco peregrinus has reached a new high in its population level in Britain. There are now at least 1,050 occupied Peregrine territories in Britain, more than have ever been recorded before. Peregrines are counted every ten years by BTO members. In 1963, the shocking results of the survey revealed only 400 occupied territories in Britain, and many of the birds were not breeding successfully. Subsequent research revealed that pesticides, such as DDT, Dieldrin and Aldrin, were poisoning the birds to death and, in addition, the calcium metabolism of the female was being disrupted. This resulted in the laying of thin-shelled eggs which were inadvertently broken by the incubating birds. The results of the early 1960s eventually resulted in the restriction and eventual banning of the harmful chemicals. The recovery was slow owing to the persistence of organo-chlorine pesticides in the environment. But by 1981 the BTO survey revealed 800 occupied breeding territories, and the first results of the 1991 survey, published in BTO News (180), show a total of 1,050 occupied territories. The recovery has been aided by a host of factors, which include volunteer protection measures to thwart egg and chick thieves, and a more responsible attitude from gamekeepers and shooters. The recovery poses some problems for pigeon-fanciers, since wild and feral Rock Doves Columba Iivia feature among the Peregrine's favourite prey species.
