The dietary and predator-prey relationships of Canis familiaris dingo were studied for 9 yr at a coastal site and for 1.5 yr at a montane site in south-eastern Australia. The percentage occurrences of items eaten were obtained from faeces, and the abundances of prey by counting water-birds, trapping small mammals, and tracking large and medium-sized mammals on specially prepared soil plots. Dingoes were also estimated by tracking.

The diet was broad but predominantly mammalian (23 species). Dietary frequencies were grouped around three weight modes, 0.1, 1.25 and 16 kg, corresponding with bush rat (Rattus fuscipes), ringtail possum (Pseudocheirus peregrinus) and swamp wallaby (Wallabia bicolor). The amplitudes of those frequencies approximately doubled from mode to mode, viz. 4, 13.5 and 28.3%, respectively. Medium-sized mammals have been recognized as the staple prey because of their dependability. Their density estimates fluctuated least among prey-groups, and track records of dingoes in the mountains were significantly related to them. Other categories of prey were supplementary (large mammals), opportune (small mammals) and scavenged.

Although there were general tendencies for dietary frequencies to follow prey abundances, significant functional and numerical responses were obtained only for water-birds (coot and swan). Their super-abundance in the mid-years of the coastal study and their highly clumped distribution were the likely causes.

Predation was disproportionately severe on mammalian prey-classes after an extensive wildfire at the coastal site. Such predation may have suppressed populations of wallabies and kangaroo for 2 yr until the water-birds became super-abundant. The prevalence of wombats in the mountains may have induced heavy predation upon other less numerous large prey. Concepts of profitability in feeding appear to apply to the dingo more than those of optimization of time or energy.

The decline in dingoes was correlated most with long-term declines in water-birds and medium-sized mammals. At the time, abundance estimates of wallabies and kangaroos were increasing and those species increasingly predominated in the diet. The ability to hunt co-operatively was apparently ineffectual in preventing decline in dingo numbers.

It is suggested that pack size is related inversely to the level of temporal instability in the environment. Frequent wildfires may prevent staple (mediumsized) and supplementary (large) prey from being abundant simultaneously, a combination thought necessary for large pack size.