Population dynamics and prey selection of native and introduced predators during a rodent outbreak in arid Australia

Abstract

We examined population dynamics and trophic ecology of a predator–prey system in the Simpson Desert, Australia, consisting of an assemblage of small mammals (body mass , 100 g) and 4 species of predators: the endemic letter-winged kite ('Elanus scriptus'), a nocturnal-hunting rodent specialist; and 3 introduced mammalian predators (dingo [Canis 'lupus dingo'], European red fox ['Vulpes vulpes'], and house cat ['Felis catus']). This is the 1st comprehensive study of the responses of both the kite and introduced carnivores to a rodent outbreak. The 3.5-year study period included a population outbreak of about 24 months duration involving 3 native rodent species. Mammalian predators and kites exhibited similar population responses. Kites immigrated into the area within 6 months of the outbreak commencing, and remained while rodent abundance was high; however, all birds left the area after rodent populations crashed within a 6-week period. Dingoes and foxes were more abundant than cats and both species increased during the outbreak. All carnivores were resident. The letter-winged kite fed almost entirely on rodents. Rodents were the main prey of the 3 mammalian predators during the outbreak; however, all species had intermediate niche breadths. Dietary overlap between the kite and each carnivore was high during the rodent outbreak. During a nonoutbreak period, predation on rodents by the red fox remained high, whereas that by the dingo declined. We estimated the number of average-sized rodents (body mass 32.65 g) eaten daily by a nonreproducing individual to range from 1 (letter-winged kite) to 6 (red fox). We also estimated that the 3 mammalian predators (combined) captured 11 times as many rodents per day as letter-winged kites. There is considerable potential for food-based competition between the kite and introduced mammalian predators, particularly the red fox and house cat, in arid Australia.