Updated 3:16pm: New research has highlighted major inbreeding problems in Little Spotted Kiwi populations in the Marlborough Sounds.

The current 50 kiwi on Long Island are all from the same two founding birds, and their offspring can't hatch chicks.

University of Otago researcher Helen Taylor says the kiwi population looks like it's growing, but that's only from the first two birds.

"Eventually, when the founding birds die and the third generation birds start to die off the population will go into decline."

"What we saw was that most of the birds were laying eggs but not hatching eggs.

"They were putting in a lot of effort and getting two or three eggs a season, but they weren't hatching."