The early re-colonisation was very slow because of contamination of the food chain by organochlorine pesticides and the activities of egg collectors. As a result, the breeding population had reached only 14 pairs by 1976. To protect the birds and increase their survival rates, "Operation Osprey" was launched. Barbed wire and electric wires were placed around the trees the birds nested in and a watch was kept over them through the night. Fifteen years later, in 1991, the number of pairs had increased to 71. In 2001, 158 breeding pairs were located, mainly in Scotland. In 2011 RSPB estimated there were between 250 and 300 nesting pairs in Great Britain.