Primary causes of kōkako decline were forest clearance by settlers and the introduction of predators such as rats, stoats and possums.

Unlike many of New Zealand's most vulnerable birds, kōkako survive in low numbers in several North Island native forests.

However, research has shown that female kōkako are particularly at risk of predation as they carry out all incubation and brooding throughout a prolonged (50-day) nesting period.

Years of such predation have resulted in populations that are predominantly male and with consequent low productivity rates.

For example, between 1991 and 1999 the breeding population of kōkako increased tenfold in Mapara Wildlife Reserve (Waikato) thanks to a series of four aerial 1080 operations.