The country's rarest species of kiwi could be losing its eyesight, say an international group of researchers.
The researchers, including Te Papa's Alan Tennyson, studied the eyes of 160 rowi kiwi living in Ōkarito forest on the South Island's West Coast.
Their paper, published in (the peer-reviewed, open access journal) BMC Biology, found a third of those kiwi were blind in one or both eyes yet the birds were remarkably healthy.
"[Kiwi] possess the smallest eyes relative to body mass of any avian species, have underrepresented visual brain regions, and have the smallest visual fields among birds," wrote lead author Christopher Murphy.
Visually impaired birds would normally struggle to find food or detect predators, he said.
However, the kiwi's more highly-developed senses of smell, touch, and hearing helped it forage for food on the forest floor, Professor Murphy said.
That meant sight was not necessary for its survival - and the birds they found were in good shape.
"It is apparent that kiwi are able to support themselves nutritionally in the complete absence of vision," he said.
The researchers suggested the kiwi were losing their eyesight as an evolutionary response to foraging at night, in the same way that many cave-dwelling creatures such as spiders and fish had lost theirs.
The researchers conceded they were unable to offer any evidence to support that claim.
Similarly, the birds could have been part of an older population, Prof Murphy said and more research was needed into why so many had lost their eyesight.
- By Michael Cropp