Diet, feeding behaviour and echidna beaks: a review of functional relationships within the tachyglossids

Echidnas are commonly known as ‘spiny ant-eaters’, but long-beaked echidnas (Zaglossus spp.) do not eat ants, whereas short-beaked echidnas (Tachyglossus aculeatus) eat other invertebrates as well as ants. The differences in skull morphology between short- and long-beaked echidnas are related to the differences in their diets, and I tested the hypothesis that there would be differences in beak length of short-beaked echidnas from populations with different diets. Published data on diet from echidnas from different parts of Australia show that echidnas from arid and semi-arid areas (subspecies acanthion) and Kangaroo Island (subspecies multiaculeatus) principally eat ants and termites, whereas the main dietary items of echidnas from south-eastern Australia (subspecies aculeatus) and Tasmania (subspecies setosus) are ants and scarab larvae. Using museum specimens and photographs I measured skull dimensions on echidnas from different parts of Australia: acanthion and multiaculeatus have narrower skulls and shorter beaks than aculeatus and setosus, with setosus being the only Australian subspecies where beak length exceeds cranium length. Australian short-beaked echidnas fall into two groups: aculeatus and setosus from the wetter east and south-east, which eat ant and scarab larvae, and the arid and semi-arid zone acanthion and multiaculeatus, with shorter, narrower skulls, and which eat ants and termites.