The marooning of populations on offshore islands can be used as a conservation technique for species threatened by introduced predators, but post-release breeding success is not always as high as expected. Following the release of Mauritius Fodies onto a partially restored islet of regenerating forest, supplementary food and control of nest parasites through the application of insecticide were used as precautionary measures to aid the establishment of a population. Nests were continuously monitored in the first three breeding seasons to inform future management decisions. The fodies built nests in taller, more mature vegetation and younger females were more likely to abandon nests before incubation started. Eggs were laid between July and February and nests made earlier in the season were more likely to fledge young. Treating nests with the insecticide carbaryl increased the probability of success, but the distance of the nest from the supplementary feeding aviaries had no effect. The number of young per female decreased each breeding season and nesting success was similar to that of fodies using exotic plantation trees on the mainland between 2002 and 2006. Future research using population models and adaptive management could lead to the withdrawal or reduction of support measures for the released population and/or the harvest of individuals to establish populations on other offshore islands.

The population of the Critically Endangered Mauritius fody Foudia rubra fell by 55% over 1975–1993 because of habitat destruction and predation. The species was believed to be dependent on a small grove of introduced, non-invasive Cryptomeria japonica trees that offered protection from nest predation. We investigated the current population size and distribution of the fody and compared nesting success in forestry plantations to that of a released population on an offshore island. The population size on the mainland has remained stable over the past 10 years, with increases in pine Pinus spp. plantations, but continues to decline in areas of predominantly native vegetation. Only 16% of pairs found were estimated to nest in native tree species. Up to 81% of nest failures on the mainland were attributed to predation but nesting success in C. japonica and pine trees was similar to that of a released population on a predator-free offshore island. The mainland population is increasingly dependent on plantations for survival and we predict this will continue. Management and protection of non-invasive exotic species, together with creation of native habitat refuges on the mainland and offshore islands can be used to increase numbers of threatened birds in areas where predator control is not feasible.