Population ecology of the southern cassowary Casuarius casuarius johnsonii, Mission Beach north Queensland

Abstract

Little is known of the ecology and population dynamics of the world’s largest avian frugivore. This study investigated the population of endangered southern cassowary at Mission Beach, northeast Australia, and examined the problems associated with determining population size and density of this keystone species. Using the results of an intensive field survey aimed at estimating absolute numbers of individual cassowaries, the appropriate sampling methodology for rare and elusive species was explored. Approximately 102 km2 of rainforest was surveyed using 346 km of search transects. Of a total of 110 cassowaries, there were 49 adults (28 male, 19 female, 2 unknown), 28 subadults, 31 chicks, and 2 independent birds of unknown status. This is approximately 35% of the adult population previously estimated for the Mission Beach area. Overall adult cassowary density was 0.48 adults/km2; the density of independent birds, i.e. adults and subadults, was 0.78 birds/km2. Mean indicative home range (IHR) for adult females and males was 2.13 and 2.06 km2, respectively. Mean IHR of subadults was smaller at 0.95 km2. It was concluded that the previous practice of surveying small areas at Mission Beach (<4 km2) has led to consistent overestimation of cassowary population density, up to six times its real number. It is shown that a sample plot between 5 and 15 km2 is necessary to approximate true cassowary density. These findings have significant application to the conservation of cassowaries in New Guinea and in the Wet Tropics World Heritage Area of Australia.