Decrease in Eggshell Weight in Certain Birds of Prey

Abstract

THE incidence of broken eggs in nests of peregrine falcon Falco peregrinus, sparrowhawk Accipiter nisus and golden eagle Aquila chrysaëtos in Britain has increased considerably since 1950. In 109 peregrine eyries examined in 1904–50, there were only three instances of egg breakage, compared with forty-seven in 168 eyries examined in 1951–66. Two of thirty-five golden eagle eyries examined in 1936–50 contained broken eggs, compared with twelve out of forty-eight examined in 1951–63. One breakage was found in twenty-four sparrowhawk nests in 1943–50, but eight in twenty-seven nests in 1951–60. Peregrines have been witnessed eating their own eggs¹, and most recent egg breakages in all three species appeared to involve parental destruction.