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The kaka (Nestor meridionalis) is an endemic parrot of New Zealand, and is nationally endangered. Conservation of the species is primarily dependent on intensive control of introduced mammalian nest predators, particularly stoats (Mustela erminea) and brushtail possums (Trichosurus vulpecula). Breeding was studied in 4 sites: Waipapa (1996-2002) and Whirinaki (1998-2002) in the North Island, and Rotoiti (1997-2002) and Eglinton (1998-2002) in the South Island. In total, 145 nests were found. The proportion of radio-tagged females that bred at a site in a given year varied from 0-100%, with most breeding occurring in years of mast-fruiting or seeding by key food tree species. Kaka nested mainly in trunk cavities of live canopy or emergent trees. Egg-laying occurred from Oct to Mar, but differed between years within sites by up to a month, and was usually 2 months later at the most southern site (Eglinton) than elsewhere. Mean egg length was 41.5 mm, mean maximum breadth was 31.5 mm, and fresh egg mass was 22.6 g or 5.65% of female body weight. Clutches consisted of 1-8 eggs, most being of 3, 4 or 5 eggs (mode = 5), and mean clutch size did not differ significantly between the sites. The female alone carried out incubation, with her mate feeding her 8-12 times a day. Overall, hatching success varied from 39-66% between sites, but it also varied between breeding seasons at each site, in part due to the level of control of introduced predatory mammals. Kaka nestlings were covered in white down at hatching, and left the nest when c. 70 days old. Even when 11-20 days old, they were left unattended at night for 20-70% of time and by day for 50-85% of time. Twice females were filmed aggressively attempting to evict stoats that had killed broods in their nest cavities. Breeding productivity (proportion of eggs that produced fledglings) in the 4 study sites varied from 19% at Whirinaki (no control of predatory mammals) to 53% at Eglinton (intense control of predatory mammals). The implications of the breeding biology of the kaka are discussed in relation to conservation management of the species.