There is an extensive cucularis capitis clavicularis muscle that is associated with the large crop. Because kakapo passed through a genetic bottleneck, in which the world population was reduced to 49 birds, they are extremely inbred and have low genetic diversity. This manifests in lower disease resistance and fertility problems: 40% of kakapo eggs are infertile. Beginning in 2015, the Kākāpō 125 project aimed to sequence the genome of all living kakapo, as well as some museum specimens – the first time an entire species has had its genome sequenced. The project is a collaboration between Duke University and the New Zealand Genomics lab in Dunedin. Before the arrival of humans, the kakapo was distributed throughout both main islands of New Zealand. Although it may have inhabited Stewart Island before human arrival, it has so far not been found in the extensive fossil collections from there. Kakapo lived in a variety of habitats, including tussocklands, scrublands and coastal areas. It also inhabited forests dominated by podocarps (rimu, matai, kahikatea, totara), beeches, tawa, and rata. In Fiordland, areas of avalanche and slip debris with regenerating and heavily fruiting vegetation – such as five finger, wineberry, bush lawyer, tutu, hebes, and coprosmas – became known as "kakapo gardens". The kakapo is considered to be a "habitat generalist". Though they are now confined to islands free of predation, they were once able to live in nearly any climate present on the islands of New Zealand. They survived dry, hot summers on the North Island as well as cold winter temperatures in the sub-alpine areas of Fiordland. Kakapo seem to have preferred broadleaf or mountain beech and Hall's tōtara forest with mild winters and high rainfall, but the species was not exclusively forest-dwelling. All kakapo that were transferred to predator-free islands in the last decades have adapted well to any changes in environment and food plants. It seems that the kakapo – like many of New Zealand's bird species – has evolved to occupy an ecological niche normally filled by various species of mammal (the only non-marine mammals native to New Zealand are ). The kakapo is primarily nocturnal; it roosts under cover in trees or on the ground during the day and moves around its territories at night.