A population of kiwi once thought to be thriving in Marlborough is being threatened by inbreeding.

Dr Helen Taylor, an expert in kiwi genetics and inbreeding, analysed a population of the little spotted kiwi on Long Island, and found poor hatching success compared to a Wellington population.

Taylor's research found nearly two-thirds of the 50-strong population were direct offspring of the Queen Charlotte Sound island's founding pair.

She said they expected to find more birds of second, third, and fourth generations.
"The overabundance of first-generation birds suggests that the damaging genetic effects of inbreeding are strongly affecting hatching, survival and possibly reproduction of the subsequent generations," she said.

The University of Otago study conducted autopsies of unhatched eggs, finding many had malformed embryos, or none at all.