Tell tails

Written by      

Samuel Purdie

Almost all of our 124 endemic lizard species are in trouble, but it seemed that the most common of them, at least, were not being too badly hammered by imported predators such as ferrets, stoats, cats and mice. Now, a new study by the Department of Conservation and Manaaki Whenua-Landcare Research suggests otherwise.

In 2014, scientists recorded the populations of three common lizards—schist geckos, McCann’s skinks and southern grass skinks—around a gully in Central Otago. The following year, a conservation group put up a mammal-proof fence around the gully and cleared it of predators. And in 2019, scientists counted lizards again, this time looking both inside and outside the fence. They used ink-laced tracking tunnels and built lovely basking spots—small, sunwarmed stacks of corrugated iron—to attract the lizards for easy totting-up.

It turned out that the populations assumed to be doing okay were just a fraction of what was possible without predators. Outside the fence, for example, the skinks’ inky footprints appeared in only 2.2 per cent of the tracking tunnels. Skinks on the inside, however, had skittered through 42 per cent of the tunnels. The geckos were booming, too. Every day, the scientists spotted an average of 17.7 in the enclosure, up from 5.2 before the fence went up.

Without predators, the geckos were also managing to hang on to their tails. Only one per cent of those inside the fence had dropped their tail, a diversion tactic deployed when they feel threatened. But among those on the outer, one in every four was tailless.

The scientists say the study shows that even apparently common species may be declining—and that fences work. They’re hoping for an “exponential population increase” in the next few years, as the first generation of lizards growing up in the sanctuary goes on to breed.