The kiwi bird's unique nocturnal behavior is linked to some altered genes that eliminate color vision and others that modify its sense of smell, according to the first kiwi genome published in the open-access journal Genome Biology. Kiwis are endangered, ground-dwelling birds endemic to New Zealand. They are the smallest and only nocturnal representatives of the ratites - a group of flightless birds that includes the ostrich and the emu. Kiwis are also unusual in that they have a highly developed sense of smell, low metabolic rate, and enormous eggs in relation to body size. However, the genetic adaptations that underpin their unique traits have so far not been well understood. A team of researchers sequenced the genomes of two North Island brown kiwi. Not only was the kiwi genome found to be one of the largest bird genomes sequenced to date, but the team also identified evolutionary changes in its genome that help explain the bird's unique adaptations to nocturnality - a behavior found in under 3% of all bird species. Lead author Dr. Diana Le Duc from the University of Leipzig and the Max Planck Institute for Evolutionary Anthropology, Germany, said: "We've seen for the first time that kiwi lack color vision, and that their olfactory receptors can probably detect a larger range of odors which may be essential for their night-time foraging. 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 kiwi gene coding for the protein responsible for black-and-white vision, rhodopsin, was found to be similar to the corresponding gene in other vertebrates. However, the team identified mutations in the green-and-blue vision receptor genes, which could render blue and green color vision absent in the kiwi.
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