Seed Dispersal by Cassowaries (Casuarius casuarius) in North Queensland's Rainforests

Abstract

Casuarius casuarius inhabits the rainforests of northeastern Australia and some of the islands to the north. It depends on fruit which has fallen from the middle and upper forest canopy. During the two-year study period diaspores of 78 plant species were found in cassowary dung. Although the germination percentage of seeds in dung were variable, some germination was observed for 70 species. The passage of most diaspores through a cassowary does not appear to greatly affect seed germination characteristics. These birds are the only extant frugivores large enough to effectively disperse many of the plant species found in the rainforests of this region. CASSOWARIES ARE LARGE (standing to 1.5 m high), powerfully built, flightless birds which are found in or near rainforests in northeastern Australia, New Guinea, and some adjacent islands (Rand and Gilliard 1967). Of the three extant species recognised, Casuarius casuarius (L.) is the most widespread and is the only species now found in Australia. They are reasonably common in the lowland rainforest north of Ingham where their presence is indicated by tracks and piles of dung. The latter are readily recognisable, consisting of up to one kg of seeds and fruit fragments (Fig. 1). Crome (1976) used these dung components to identify the plant species contributing to their diet. The observation that seeds frequently germinated within the dung piles (Fig. 2) prompted the present study aimed at assessing the role of cassowaries in dispersing rainforest plant species. Although Ridley (1930) provides several reports of cassowaries dispersing seeds of some forest species on Ceram and the Aru Islands, the cassowary was not incduded in Snow's recent world survey of tropical frugivorous birds and their food plants (Snow 1981) and except for the notes of Crome (1976) and Frizelle (in White 1913) very little seems to be known of this bird's biology.