A model for the effects of fire and fragmentation on the population viability of the Splendid Fairy-wren

Abstract

Computer simulation was used to model the relationships between four environmental factors (nest predation, brood parasitism, fire and rainfall) and the probability of local extinction in hypothetical populations of Splendid Fairy-wrens in differently sized patches of habitat. The parameters of the model are based on the results of a long-term (17 year) study of the species at Gooseberry Hill, Western Australia. Two fire scenarios are modelled ? wildfire and controlled burning. The model predicts that wren populations in small patches (less than about 2 000 ha in area) stand a high risk of local extinction if exposed to environmental conditions similar to those experienced at Gooseberry Hill, in particular the frequency and extent of wildfires (Gooseberry Hill fire probability 20%). It is suggested that: (a) urban reserves aimed at conserving small sedentary species such as the Splendid Fairy-wren should contain at least 2 000 ha of suitable habitat if there is a high risk of wildfire (minimum viable population for wrens under these conditions, 500 breeding females); (b) the integrity of existing reserves and parklands should be protected from further fragmentation since the likelihood of local extinctions will increase as the carrying capacity of the habitat declines; (c) management of existing reserves and parklands should be directed toward limiting the environmental pressures impacting populations of native species, in particular the frequency and extent of fire and the numbers of feral nest predators. If the probability of fire can be limited to five per cent or less, Splendid Fairy-wren populations in patches as small as 400 ha (100 breeding females) may be viable in the long term.