Kākāpō come in two shades of green: moss and olive.
The current 250-strong population of our flightless and sweet-smelling night parrot gains no obvious benefit from this, but researchers recently discovered that the colour switch was once a life saver.
They scoured the genome sequences of 168 birds, representing nearly all living kākāpō at the time, for any genetic hints of how and when the colour difference evolved. It turns out kākāpō were originally moss green, and the olive plumage appeared only some 1.93 million years ago, just as two large predatory birds emerged: Haast’s eagle and Eyles’ harrier. Both raptors were visual hunters, out during the day when kākāpō would have been asleep, hiding in the bush.
The colour difference is very subtle, says Lara Urban, a principal investigator at the Helmholtz Pioneer Campus in Germany, who led a research collaboration with New Zealand scientists, Ngāi Tahu and the Department of Conservation’s kākāpō recovery team.
“It’s only because of the keen eyes of conservationists and iwi as kaitiaki of this endangered species that we know there is such a colour polymorphism.”
University of Auckland biologist Anna Santure says the genetic basis for this could only be discovered thanks to the multiple genomes available. “The idea to sequence the whole species was to capture all of the genetic diversity and to look how it associates with different characteristics,” she says.
The team was able to pin the change to particular genetic variants in the population, and to a gene known for the early development of teeth in mammals. “In this case, it’s determining a very slight difference in the structure we find in the olive versus green feathers,” Santure says.
Electron microscopy has indeed confirmed that the difference in colour is not caused by pigments but by small changes in the structure of feathers, which means they reflect slightly different wavelengths of light.
A “neat part of the research” was realising how long both variations have been present, Santure says. “It’s unusual for a characteristic like this to persist for nearly two million years.”
Usually, any new beneficial trait would eventually take over, but the two colours remain roughly equally represented among kākāpō, even after their avian predators went extinct about 600 years ago.
Computer simulations suggest an interesting cycle. “We think the predators would have been scanning the landscape, looking for tasty kākāpō. When the rare olive variant arose, they wouldn’t have known to look for it, but as it became more frequent (because they were eating more of the green birds), they learnt to look for the olive birds.” The predators’ preference then swung back and forth as one colour became rarer.
Back then, kākāpō were plentiful. But by 1995, their numbers had dwindled to 51. During “this extreme bottleneck, it was probably just luck that we still had both colours”.
Without intervention, the variation could be lost within 30 generations, but given the species’ active management and precisely recorded breeding, it’s unlikely this will happen, even though the colours don’t seem to have any implications for the birds’ health today.
The conservation effort aims to preserve as much diversity as possible, Santure says, and the colours are part of what “makes each kākāpō unique and gives them their personality”.
The findings follow earlier research that analysed the same suite of genomes to determine factors that influence growth rates and susceptibility to disease. Ultimately, the kākāpō team wants to better understand the underlying genetics so they can focus their efforts on chicks that need the most care.
So the team will keep sequencing new generations. “We can predict what the offspring might look like based on the parents’ genomes, but that becomes less predictable as we go through a number of other breeding cycles. Those predictions get better and better the more individuals you sequence.”
