Ecogeographic and Temporal Variation in the Eggs and Nests of the Peregrine, Falco peregrinus, (Aves : Falconidae) in Australia

Abstract

Latitudinal and temperature-related clines in egg size were found for the peregrine falcon, Falco peregrinus, in Australia, egg size increasing with increasing latitude and decreasing temperature. The breakdown of these clines since the 1940s corresponded temporally with the introduction of DDT to agriculture and with greater intensification of land use. In eggs collected since the 1940s, the clines were still present north of 33°S. and in areas where the mean maximum September temperature was e21°C, but not south of 34°S. and in areas of mean maximum September temperature < 21°C. Mean clutch size was 2.9 (range 1-5); without evidence of clines. Most eggs were collected in September in south-eastern Australia. The timing of the egg-laying period was correlated with latitude and temperature, corresponding to the seasonal influx of migrant prey species and the breeding season of major prey species. The geographical distribution of cliff nests, stick nests and tree-hollow nests is discussed; the use of hollow trees appears to be restricted geographically. Eggs from some tree-hollow nests were larger than those from other types of nest.