Native falcons breeding at a Wellington wildlife sanctuary have been killing other native birds.
The brown falcons (karearea), which are featured on the $20 note, are about the size of a feral pigeon.
The birds began nesting in the Zealandia sanctuary, in Karori, last year and have eaten both native and introduced birds.
Zealandia sanctuary trustee Dr Colin Miskelly says because the endangered falcons need such a large range they were never on the park's breeding wish-list.
Their arrival and abundant breeding has been a mixed blessing, he says. They have so far eaten a bellbird - a native - and some blackbirds and chaffinches.
Colin Miskelly says there is little chance falcon numbers will increase dramatically because the territory is not big enough.