The feeding ecology of the dingo : III. Dietary relationships with widely fluctuating prey populations in arid Australia: an hypothesis of alternation of predation.

Changes in the diet of dingoes (Canis familiaris dingo) in response to measured fluctuations of prey populations were followed over 7 years. The study began after great rains had broken a long drought. Eruptions of rodents and rabbits followed, but some prey were always either relatively abundant (live cattle) or scarce (red kangaroo, lizards, birds). Cattle carcasses were increasingly available during a subsequent drought. Small and medium-sized prey, rodents (26%), lizards (12%) and rabbits (56%) were preferred, probably because they were easily caught. Only rabbits were caten consistently regardless of density. By contrast, large prey were eaten in relatively large amounts only during drought, with initial emphasis on red kangaroos (15% overall) and then cattle (17%) mostly as carcasses. The diet was functionally related to the respective abundances of all major prey species, but the relationship shifted during drought when predation on low populations was most severe. There was evidence that growth of resurging prey populations were suppressed by predation. Diets of dingoes did not differ significantly with age or sex. An hypothesis of 'alternation of predation' is presented: dingoes feed sequentially on prey of increasing size (rodents, rabbits, red kangaroos, cattle) in response to rainy periods and subsequent droughts, meanwhile always concentrating on the staple prey (rabbits). The fluctuating abundances of small and medium-sized prey determined not only their own relative availabilities but also that of large prey, and hence determined the diet of the dingo at any time. Prey availability (catchability, accessability) appeared to be more important than prey abundance (numbers, biomass), and the dingo's flexible social organisation allowed versatility in hunting strategies and defence of resources. We conclude that dingoes do not always forage most efficiently as optimal foraging models predict because of the constraints imposed by the capricious environment in arid Australis, where prey availability fluctuates greatly and becomes limited and clumped in drought, so that dingoes may be faced with outright starvation. Instead we conclude that dingoes utilise a conservative feeding strategy and adopt any behaviour which provides at least a threshold quantity of energy or nutrient as part of a trade-off with other competing ecological requirements.