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

The long-suspected finding comes from new research revealing how the 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 insights have been revealed in a study, published today in the journal Genome Biology, which mapped for the first time the genome of the North Island brown kiwi - the most common species of the endangered bird.

Kiwi have proven curious creatures to scientists for many reasons, among them their highly developed sense of smell, low metabolic rate, and enormous eggs in relation to body size.

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How they have developed genetically to have these characteristics, however, hasn't been well understood.

When a team of German researchers sequenced the genomes of two kiwi, they discovered not only that it was one of the largest bird genomes sequenced to date, but also strange evolutionary changes that could help it explain how it gradually adapted to nocturnality.

This behaviour is observed in less than three per cent of all bird species.

"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 and the Max Planck Institute for Evolutionary Anthropology.

"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 to 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.

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The researchers estimated the onset time of these changes to around 35 million years ago, suggesting that the kiwi adopted its nocturnal lifestyle shortly after the arrival of its ancestor in New Zealand.

At the time the kiwi arrived other ratite birds, the moa, already inhabited New Zealand.

These now extinct birds, of which one species was over three metres in height, are thought to have monopolized food sources during the day, forcing the kiwi to adopt an alternative nocturnal lifestyle.

Kiwi are unique among birds in having nostrils present at the end of their long beaks and it has long been thought they are more similar to mammals than birds in their reliance on tactile and smell senses for foraging.

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

Nocturnal animals tend to have low energy metabolism, and kiwi have the lowest metabolic rate among all birds.

In the genome, the team found enriched changes in genes related to energy expenditure, reserves and metabolic processes, which may also be linked to this nocturnal lifestyle.

The study marks the latest leap in our understanding of kiwi and its clouded history.

Last year, DNA sequencing revealed the kiwi was closely related to the extinct, 2.3m tall elephant bird, a native of Madagascar, re-writing a back-story that had the kiwi's ancestor likely flying in from Australia.

The country breathed a collective sigh of relief at the fact our kiwi was no Aussie.

Dr Tammy Steeves, a conservation geneticist at Canterbury University, said the new findings from Germany were exciting.

Of the more than 10,000 bird species worldwide, a mere 50 of them had a readily available genome.

"Given that bird genomes are small, compact and highly conserved, the publication of the kiwi genome will help pave the way for a new era in the conservation of bird biodiversity in New Zealand."

Using a high quality genome like that generated for the North Island brown kiwi would allow for the development of species-specific genomic resources, she said.

"These resources will provide a more accurate representation of genome-wide diversity and better inform conservation management strategies to minimise the loss of genomic diversity, particularly for threatened birds like the North Island brown kiwi."

Last year, the Department of Conservation warned that the kiwi could become extinct within our grandchildren's lifetime if there was not intervention.

Wild kiwi numbers were falling by 2 per cent each year and, at this rate, the bird could be wiped out on the mainland within the next generation.

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

But despite such conservation efforts, North Island brown kiwi are still at high risk of extinction, Dr Le Duc said.

"We made a first estimate of the diversity of the kiwi genome by comparing the sequence of two individuals, and it appears to be as low as that of inbred birds.

"This is an important indication of the level of the threat, and we expect further insights from the genome to help in developing conservation management strategies."

Dr Lara Shepherd, a genetics researcher at Te Papa, expected the new data would not stop the decline of wild kiwi, which could largely be blamed on predation by introduced mammals.

"New funding for kiwi predator control announced in this year's budget will hopefully halt this decline."