Chevron Skinks the shy locals of Great Barrier Island by Ben Barr

Environmental News Issue 16 Spring 2008

Q: What native animal is found in trees but can’t fly, can hold its breath underwater and was lost longer than the takahe?

A: Niho taniwha — the riddle of the chevron skink.

It all started in the heady days of the 1970’s. While most New Zealanders were busy growing long hair and listening to psychedelic music, a group of dedicated conservationists in the backblocks of Great Barrier Island were busy rediscovering the most intriguing and enigmatic skink of them all — the Niho Taniwha or chevron skink (Oligosoma homalonotum).

The chevron skink is one of the most attractive and unique lizards in New Zealand and is only known from two islands in the Hauraki Gulf — Great Barrier and Little Barrier Islands. The chevron was first described in 1906 but was subsequently lost to science for the better part of last century. The chevron spent its adolescent years known as the Great Barrier skink until a lone animal was found deep in the misty gullies of Hauturu. Great Barrier Island continues to be the stronghold for chevron skinks and is the location where this revered and fascinating creature is slowly giving up clues to rangers and scientists as to how it spends it days.

A dedicated D.o.C led research programme was initiated in the 1990’s to learn more about the chevron skink. At that stage there had only been 100 or so records and people only had a faint idea where they lived and how to catch them. The team was led by Keri Neilson and included current Great Barrier Island biodiversity ranger Halema Jamieson. The team made enormous headway into understanding some key facts about the chevron skink with the most important discoveries being; they tend to live very close to streams in and around debris dams because they lose water easily; and the best way to catch a chevron is a fish trap baited with banana placed in a stream debris dam. It sounds like simple stuff but it has made subsequent research a walk in the park.

Relaxing by a crystal clear forest stream and having lunch in the dappled light I thought to myself “these chevrons are onto it, why don’t I live down here?” My question was answered the very next day when a huge rain bomb unleashed over the island bringing 50mm of rain in just a few hours, and turning the normally tranquil streams into torrents. Many of the skinks’ debris-dam homes were completely submerged and some had been swept away. I started to fear for the chevrons. I hastily checked on 4 animals I was radiotracking, and to my amazement 3 of them had climbed up amongst dead fronds in the crowns of streamside silver ferns. As soon as the flood subsided and the sun came out, the chevies were back down on the ground in their usual retreats. A month later and the Barrier received another torrential downpour and once again the chevrons made for the trees to escape the inevitable floodwaters. During these flooding events I searched in random fern crowns to see if I could find any other chevrons (seeing as 75% of mine were up there). To my surprise I found one on my third attempt. Two floods and eight search hours later and I had 6 chevrons ranging from just born to fully-grown adults. In comparison, similar searches during dry episodes revealed no chevrons at all. This discovery makes sense of their striking patterns which looks remarkably like a dead fern frond; indeed they are very difficult to see when hiding in the fern crowns (it’s got to be in here somewhere!). It turns out I had no need to worry at all… these skinks have been escaping floods for thousands of years, and have even evolved a clever disguise that keeps them safe from our native avian predators. If worst comes to worst they can also hold their breath as an escaping skink showed me when he jumped into the creek and hid between some rocks underwater.

The chevrons may not be so good at being undetected by introduced predators. Two adult chevrons were found this year that had been attacked by rats - luckily they survived but sustained some nasty head injuries. In addition many of the chevrons in unmanaged areas have lost sections of their tails. This is probably due to rats, as in privately owned areas with intensive rat control (Glenfern Sanctuary) the skinks are in better condition overall. There are also a lot more juveniles and sub-adult skinks in these areas, which suggests a recovering population.

The future of the chevron skink is starting to look brighter, we now need to focus on making sure the population on Great Barrier Island is maintained by establishing what animals are threatening their survival. We also need to make sure the Hauturu chevron population is alive and well as to date there has only been two animals found there.