The mortality of British Grey Herons

Abstract

Grey heron [Ardea cinerea] mortality rates were estimated for 3 separate time periods (1909-1941, 1942-1954, 1955-1975) and within each, for 3 separate age classes. In the first of these periods mortality was 69.7% for 1st-yr birds, 30.9% for the 2nd yr and 24.7% annually thereafter. By the 3rd time period the corresponding figures were 55.9, 46.9 and 30.3%. First-yr survival has improved (coinciding with the advent of legal protection in 1954), while that for older birds has deteriorated (coinciding with the increased usage of pesticides). These changes are also reflected in the monthly distribution of recoveries and reported causes of death. The incidence of shooting has declined, and more deaths now occur during the breeding season. Productivity calculations show that an increased proportion of 1st-summer birds need to join the breeding population for numbers to be maintained. It is fortunate that legal protection (which especially helped 1st-yr birds) was given early in what proved to be the pesticide era.