PATCH USE AND PREY DEFENSE IN A MAMMALIAN MYRMECOPHAGE, THE ECHIDNA (TACHYGLOSSUS-ACULEATUS) (MONOTREMATA, TACHYGLOSSIDAE) - A TEST OF FORAGING EFFICIENCY IN CAPTIVE AND FREE-RANGING ANIMALS

Echidnas (Tachyglossus aculeatus) in wheatbelt reserves in Western Australia are primarily termite- and ant-eaters. Using captive and free-ranging animals, we tested whether echidnas respond to high density patches of these prey and also to differences in their mechanisms of defence. When feeding on termites, free-ranging echidnas generally adjusted their foraging effort in response to prey abundance, increasing their rate of energy intake by digging deeper and allocating more time to patches where prey were abundant. Such efficient foraging occurred irrespective of whether termite defence was mandibulate, chemical, or a combination of both, as in Amitermes neogermanus. Echidnas invested little effort in species of Drepanotermes in the field despite their abundance at local food patches, probably because the soldiers are large and aggressive and produce copious quantities of pungent defence secretions. Echidnas also avoided Nasutitermes exitiosus in the field but ingested other species with chemical defence such as Tumulitermes. Captive echidnas decreased their foraging effort on N. exitiosus only when soldiers were abundant (almost-equal-to 400 per unit area) and the soldier to worker ratio was high (80:20), hence avoidance of this species by free-ranging echidnas may reflect the species' ability to mobilize quickly large numbers of soldiers to colony breaches. When feeding on ants in the field, foraging effort and prey energy in food patches were not correlated, possibly because ants responded rapidly to colony breaches by emerging to meet the predator. More extensive soil excavations by foraging echidnas to capture ants were thus unnecessary, minimizing foraging effort. Captive and free-ranging echidnas rejected ants greater-than-or-equal-to 7 mm (except in the presence of energy-rich eggs), and > 10 mm long, respectively, reducing foraging efficiency to zero when encountering such prey. With such exceptions, the results suggest that echidnas make efficient use of patchily distributed prey and generally adjust their foraging efforts to match actual energetic returns.