Two-four pinkish-grey eggs are laid in cup nests c.13 m (range 3-25 m) up trees. Fledged young usually remain in parents' territory for a few months, up to a year, and continue to be fed by both parents.
Behaviour and ecology North Island kokako defend large territories year-round by complex singing, including the longest known duetting of any songbird in the world.
Food reduction mainly by possums and predation by stoats are unhelpful secondary factors.
All current populations must be continually managed against introduced mammal pests, either by repeated pest control on the mainland, or by vigilance against pest invasion on islands. Length: 38 cm Weight: 233 g (male), 218 g (female) Similar species: Tui, Black-faced cuckoo-shrike A large songbird with a blue-grey body, striking black mask and small rich blue wattles that grow from the base of the bill, long strong legs and a long down-curved tail.
The largest populations, with more than 100 pairs each, are in Pureora Forest, Hauturu (Little Barrier Island ), Te Urewera, Mapara (Waikato), Rotoehu (near Rotorua) and Hunua Ranges.
Other large populations ( 50 prs) are at Mataraua/Waima (Northland), and Kaharoa-Onaia near Rotorua, and there are 14 other smaller populations.
Ship rats and possums are routinely targeted by trapping and poisoning so that their numbers are low for the duration of the breeding season (November to February). The sexes are alike; juveniles have pink or lilac wattles.
Food supply influences the number of breeding attempts that kokako make, but nest predators determine the outcomes of these attempts.
Breeding North Island kokako typically raise one brood during November-February, after which they moult.
In occasional years of good food supply, the breeding season may last 6 months and up to three broods can be raised. Young fledge at 32-37 days old, and so nests are vulnerable to predation for about 7 weeks.
Typically, when seen backlit in forest, kokako seem dark-plumaged and neither mask nor wattles are seen.
They have long, strong legs and a long down-curved tail.
Breeding pairs and unpaired singles defend 4-25 ha territories year-round by singing, which limits density.