Department of Conservation rangers say it has been a brilliant breeding season for the birds in Waipoua Kauri Forest after an aerial 1080 drop.
DoC blitzed 15,000 hectares of native forest with the poison last spring.
The department's Waipoua manager, Maerene Hardy-Birch, says rat numbers were at plague levels before the drop, with 55 rodents being caught per 100 traps. She says that has dropped to just 1.5 per 100 traps.
Mrs Hardy-Birch says final figures on the possum kill are not in yet, but the results are evident, with plant species that have not flowered in years because of predation now producing fruit.
She says Waipoua's endangered kokako have reared chicks successfully this summer, and the numbers are up from just eight birds in the late 1980s, when poison drops began, to 42.