Kiwi colour-blind, gene study finds

Scientists say the changes could help explain kiwi nocturnality. Photo / NZME

Mutations in genome from about 35 million years ago point to vision changes but also strong sense of smell.

Not only is our quirky national bird flightless - it's also colour blind.

The finding comes from new research revealing how the endangered kiwi evolved its sense of smell and colour 35 million years ago to help it cope with its nocturnal life sniffing around the undergrowth at night.

The study published in the journal Genome Biology mapped, for the first time, the genome of the North Island brown kiwi - the most common species of the endangered bird.

After sequencing the genome of two kiwi, the German scientists who led the study uncovered evolutionary changes that could help explain why it was among the 3 per cent of bird species that have adapted to nocturnality.

"We've seen for the first time that kiwi lack colour vision, and that their olfactory receptors can probably detect a larger range of odours which may be essential for their night-time foraging," said study lead author Diana Le Duc, of the University of Leipzig. "These adaptations seem to have happened around 35 million years ago, soon after their arrival in New Zealand, probably as a consequence of their nocturnal lifestyle."

The gene responsible for black and white vision, rhodopsin, was found to be similar in other vertebrates.

However, the team identified mutations in the green and blue vision receptor genes, which could render blue and green colour vision absent in the kiwi.

The changes in kiwi vision and smell were consistent with changes thought to occur during adaptation to nocturnal lifestyle in mammals.

The kiwi genome also showed significantly higher diversity in smell receptors than other investigated birds, suggesting that they may be able to distinguish a larger range of odours.

Last year, the Department of Conservation warned that without intervention the kiwi could become extinct within our grandchildren's lifetime.

This year's Budget included a special $11 million allocation for kiwi conservation, with an aim to turn a 2 per cent decline rate into an annual increase as soon as possible.

The organisation Kiwis for Kiwi - which lost a major corporate backer this week after BNZ announced it would be ending its sponsorship - has also been battling to save the species.

Dr Le Duc said that despite conservation efforts, North Island brown kiwi were still at high risk of extinction.

"[The diversity of the kiwi genome] appears to be as low as that of inbred birds," she said. "This is an important indication of the level of the threat."

Our national bird

• Thought to have descended from a small flying bird which probably flew here from a source population in Antarctica at a time the continent was more hospitable.

• Has one of the lowest metabolic rates and the largest egg-to-body weight ratios of any bird. The egg averages 15 per cent of the female's body weight.

• Are largely nocturnal and are most commonly forest dwellers, making daytime dens and nests in burrows, hollow logs or under dense vegetation.

• Now found to be lacking colour vision but have an unusually high diversity of smell receptors - traits it evolved soon after its ancestor arrived in New Zealand around 35 million years ago.