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A breakthrough in why eggs from one of the world's most endangered birds fail to hatch could provide a lifeline for the species.
Researchers found that kākāpō embryos were failing early in development as a likely result of genetic issues, allowing conservationists to better plan a breeding programme to save the birds.
Scientists have discovered why the world's most endangered parrot is so difficult to breed successfully.
Researchers studying the kākāpō, which number just 201 individuals, found that many embryos were failing early in development probably as a result of inbreeding. This overturns previous suggestions that males suffered from low fertility.
The researchers hope that this knowledge will help organise the breeding programme so that the birds with the greatest chance of success can be mated.
Dr Jodie Crane, a co-author on the study who is working to help kākāpō populations recover, says, 'Kākāpō are an iconic species across Aotearoa New Zealand, and a taonga (treasured) species for Ngāi Tahu [the principal Māori iwi on the country's South Island].
'Since our conservation program began, hatching failure has been a major barrier to recovery. Collaborations on studies like these are crucial for solving the challenging conservation problems ahead.'
The research, led by British and New Zealander scientists, was published in Animal Conservation.
The kākāpō is a species of ground-dwelling parrot native to New Zealand and its surrounding islands. It feeds on a wide range of seeds, fruits and roots and can live for up to 60 years.
The birds were initially widespread across the country, but began to decline when humans first arrived around 750 years ago with Polynesian settlers hunting the birds and the introduction of rats. The arrival of Europeans in the 1800s accelerated the decline of the species with the introduction of more invasive species, as well as widespread habitat destruction.
By 1995, there were only 51 kākāpō left in existence. A concerted effort following the establishment of the Kākāpō Recovery Plan saw the birds moved to four small islands off the coast of New Zealand where invasive species had been eradicated. Populations of the bird have now begun to grow.
However, the small number of individuals left in the 1990s meant that the population went through a genetic bottleneck, where most of the species' genetic diversity was lost.
This was exacerbated by inbreeding, which can cause negative traits to build up through a process known as inbreeding depression. While the kākāpō has previously been found to have eliminated many negative traits by the process of genetic purging, this still significantly reduced their genetic diversity.
Together, these processes have impacted the kākāpō's ability to breed, with over 60 per cent of eggs failing to hatch. This has previously been attributed to low fertility in males, with efforts such as artificial insemination being used to try and tackle the problem.
However, researchers wanted to check if these assumptions were accurate, and if not, what else could be done to ensure that the kākāpō breeding programme is as effective as possible.
All kākāpō eggs are currently cared for by conservationists in artificial incubators, with the birds given fake eggs to care for before the chicks are hatched. Any eggs which showed no signs of development were taken from the incubators after five days and their contents analysed.
The researchers found that rather than the eggs not being fertilised, the major cause of eggs failing to develop was the death of the embryo before development. This accounted for 36% of all eggs hatched that year, with embryos dying at later stages of development bringing the number to almost half.
Of the eggs which did develop, the researchers found that embryos were more likely to fail in a kākāpō's first clutch, rather than the second. In addition, there was some evidence that artificial insemination may improve the chances of successful fertilisation, with further trials suggested to confirm this one way or the other.
As an additional benefit, the research also allowed the scientists to identify which kākāpō are infertile. Each bird is fitted with a transmitter that activates when a female is nearby and the bird is active, indicating that it might be mating.
The results suggest that around five of the 31 adult males are probably infertile, while almost all females were fertile. Further research is proposed to explore whether inbreeding is responsible for their infertility, and which individuals should be bred together to give the best chance an embryo will survive.
The study adds to a growing body of knowledge about the kākāpō and its breeding behaviour. The birds breed in large groups known as leks, where males compete to attract females. These normally take place in response to food availability, particularly during masting events, when trees produce large amounts of fruit every few years.
To complicate things further, the timing of these events is affected by temperature. In 2018, the masting took place earlier than ever before which allowed for two rounds of egg laying. Success was lower in the first round, suggesting that the kākāpōs may not have been quite ready to breed.
In future, researchers believe that climate change could cause these earlier events to become more common, adding another complication into the conservation of this critically endangered bird.