Effect of Age at Release on the Susceptibility of Captive-reared Malleefowl Leipoa ocellata to Predation by the Introduced Fox Vulpes vulpes

Abstract

Captive-reared juvenile Malleefowl Leipoa ocellata (3-5 months old) experimentally released into Yathong Nature Reserve did not survive. From the first day after release Malleefowl were found dead, and mortality continued at a rapid rate until none remained alive: 50-58% were dead within 7 days; 83-96% were dead within 36 days; and none survived longer than 104 days. Predation by the introduced Red Fox Vulpes vulpes was the principal cause of mortality, accounting for at least 50% and perhaps as many as 92% of young Malleefowl. Twelve older captive-reared sub-adults (14-28 months of age) experimentally released into Yathong Nature Reserve fared somewhat better; three survived longer than 428 days. Again, predation by foxes was the chief cause of mortality. Mortality was particularly high during the first week following liberation, but the two age classes differed in their long-term survival. One third of sub-adults survived to breeding age (2.5 years), while no juvenile survived its first year. This implies a decrease in the vulnerability of Malleefowl to foxes between the first and subsequent years of life. Predation by foxes remained the major cause of mortality among sub-adults. Fox predation may well threaten the continued survival of Malleefowl in New South Wales because they killed sub-adult Malleefowl of a weight comparable to that of many adults, which suggests that the duration of vulnerability to foxes is protracted. Furthermore, this threat is not confined to the fragmented remnants of mallee vegetation within the wheat-belt but extends to Malleefowl populations in the remaining large expanses of mallee, remote from agriculture.