Tuatara central

Stephens Island, with patches of regenerating forest clearly visible. Photo / Hilary Miller

This post originally appeared on Sciblogs.co.nz.

This little guy lives on Stephens Island in the Marlborough Sounds, and is affectionately known as "tree tut" to the Victoria University researchers who frequent the island. Because he lives in a tree, of course. His tree is along the pathway between the house occupied by the DoC rangers and the house where the researchers stay, so he has plenty of passing foot traffic to keep an eye on.

Stephens Island is tuatara central, home to a staggering 30,000 - 50,000 individuals. Given that the island is only about 150 ha in size, this means that tuatara are EVERYWHERE on the island and it is sometimes difficult to avoid treading on them.

Stephens Island has an interesting history, which may have partly contributed to the high densities of tuatara found there. A lighthouse was constructed on the island in 1893, and three houses were also built to accommodate lighthouse keepers and their families.

During World War II a radar station was set up there, and an accommodation building known as the "Palace" was constructed. The Palace is still there and these days serves as a lab and storage shed.

The clearing of land for the construction of the lighthouse and houses, and the introduction of cattle and sheep decimated the Stephens Island forest, and photos of the island from 50 years ago or so show barren hillsides with only a few remnant patches of bush.

However, for the last 20 years a revegetation program has been in full swing and the forest is returning. The lighthouse was automated in 1988, and the last lighthouse keeper left the island in January 1989. The last sheep left the island in 2005, and today the only permanent human presence on the island are the DOC rangers, who live in one of the old lighthouse keeper's houses.

Despite the human settlement and rampant habitat destruction, the only introduced predators that made it to the island were the lighthouse keeper's cats. These cats decimated some of the local wildlife, including the Stephens Island wren, an unusual flightless passerine which famously went extinct virtually as soon as it was discovered.

However, the tuatara population escaped virtually unscathed and cats were eradicated in 1925 after only about 30 years on the island. Ironically, the clearing of forest on the island may have actually increased tuatara numbers, by increasing the availability of suitable nesting sites in open areas. The island currently appears to be above its carrying capacity, and once the forest regeneration is complete tuatara numbers may decrease somewhat.

Dr Hilary Miller is a postdoctoral researcher at Victoria University of Wellington, where she researches the evolutionary genetics and genomics of New Zealand's native reptiles and birds. You can read her work and that of 35 scientists and science writers at Sciblogs.co.nz, New Zealand's science blog network.