The Peregrine Falcon, Falco-Peregrinus-Macropus S, in Tasmania .1. Distribution, Abundance and Physical Characteristics of Nests

Abstract

Peregrine falcons occur throughout Tasmania, their breeding distribution being essentially a contraction of their sighting distribution. In a study lasting from 1973 to 1986, we came to know the exact location of 108 nesting territories and the approximate whereabouts of 25 more. During the first half of the study 60% of nesting territories were occupied and about 50% were active (eggs laid); by 1986 these values had increased to 75-80% and nearly 70% respectively. The number of breeding pairs rose from 59 to 92, averaging 72. Most occurred in high-density clumps of from five to ten pairs, within which active eyries were regularly and potential eyries randomly distributed (mean G-values 0.88 and 0.46). Densities varied considerably between clumps, from mean nearest-neighbour distances of 5.7 km, and 2.08 pairs per 100 km2, in a river gorge, to 18.4 km and 0.33 pairs per 100 km2 in a group of islands. Areas with the highest density tended to have the most regularly spaced active eyries. Of all pairs, 85% were in the north-eastern half of the State; the overall mean densities in the north-eastern and south-western halves was 0.18 and 0.032 pairs per 100 km2 respectively. All recent nestings were on natural cliffs, half of which were sandstone; half were in sheltered positions; 15% were on offshore islands, and coastal nests were usually associated with nearby islands. Most eyries and nest sites faced north and/or east. Cliff eyries averaged 48.6 m in height, and in most areas there were three or four times as many potential as active eyries; lack of suitable cliffs is the main limit to breeding in only 2.7% of Tasmania. The upper altitudinal limit to breeding is about 900 m, which excludes 2.5% of the State.