Variation in Peregrine Falcon Eggs

Abstract

Abstract Eggs collected from captive and wild Peregrine Falcons (Falco peregrinus) were used to examine variation in eggshell thickness, length, breadth, and initial weight to resolve questions about eggshell data from wild falcons. For captive falcons, shell thickness of first clutches did not change over the years a falcon laid or with embryonic development. Eggshells in third clutches, but not second clutches, were significantly thinner than those from first clutches. Greatest variation in shell thickness existed between eggs within a clutch and did not differ significantly between wild and captive eggs. Entire clutches of wild falcons should be represented in future studies to maximize the chance of obtaining a representative sample in regard to shell thickness. Egg size (L, B, and fresh weight) decreased over the years a captive falcon laid. A significant decrease in size (B and fresh weight) also occurred in second and third clutches laid the same year. Ratcliffe's Index generally appeared to be a reliable indicator of shell thickness in captive-laid eggs.