Te Papa’s Curator of Terrestrial Vertebrates Dr Colin Miskelly visited Taranga for a week in December 2010 as part of his research into the life and fieldwork of the naturalist Edgar Stead. Here, Colin describes the reptiles found on the island, along with reptile records from surrounding islands, and the potential for reptile recovery and restoration following the eradication of Pacific rats (kiore) on Taranga in 2011.
Eleven reptile species have been recorded from the Hen & Chickens group of islands, with seven of these recorded from Taranga (500 ha), the largest island in the group. None of the species is confined to the group, with Towns’ skink (Oligosoma townsi) having the narrowest range, occurring also on the nearby Mokohinau Islands and Little & Great Barrier Islands.
The abundance and diversity of reptiles on the islands around New Zealand is largely determined by the current or former presence of rodents, in this case kiore (Rattus exulans). At the time of my visit, kiore were present on Taranga and also on Mauitaha (West Chicken; 24 ha) and adjacent Araara Island (2 ha). They had been eradicated from Whatupuke (198 ha) in 1993, Lady Alice Island (240 ha) in 1994, and Coppermine Island (75 ha) in 1997. Kiore will remain on Mauitaha and Araara by agreement between Ngatiwai (tangata whenua) and the Department of Conservation. Rats were never present on other small islands in the group including Sail Rock, Wareware, Muriwhenua, Pupuha and Middle Stack (the latter lies between Lady Alice Island and Whatupuke), all of which were important refuges for lizards.
I saw six species of reptiles on Taranga during my visit – tuatara, two gecko species and three skink species – none of which was abundant. The nine tuatara (Sphenodon punctatus) seen were all at high altitudes, and were among about 50 adult animals known to have survived rat presence on the island. No juvenile tuatara have been seen on Taranga, but they are abundant on the three largest Chicken islands now cleared of rats (i.e. Lady Alice, Whatupuke and Coppermine Islands). There is strong circumstantial evidence that kiore prey on tuatara eggs and young, but this has not been observed directly.
Five Duvaucel’s geckos (Hoplodactylus duvaucelii) were seen during four nights of searching coastal rocks near Dragon Mouth Cove on Taranga (none was seen under forest). All five had re-grown tails, as is often the case when lizards co-exist with rats or other predators. Lizards (and tuatara) can voluntarily shed their tails in response to a predator attack, leaving the predator with a snack while the reptile escapes. Their tails eventually re-grow, but always differ in markings from the rest of the animal (contrast with images of Duvaucel’s geckos from the rat-free Poor Knights Islands, and after nine years of no rats on Ohinau Island). Duvaucel’s geckos also survived in low numbers on the three Chicken islands cleared of rats, and are now abundant there.
Two Pacific geckos (Dactylocnemis pacificus) were found under rocks around the coast of Taranga (at Stead Bay and Pukanui Bay). Elsewhere in the group, Pacific geckos survived on rat-free Sail Rock, Wareware, Muriwhenua and Pupuha Islands, and were translocated from Pupuha to Lady Alice Island in 1997-98.
Four Suter’s skinks (Oligosoma suteri – also known as the egg-laying skink or diving skink) were seen along the boulder beach at Dragon Mouth Cove, including two foraging at night. The habitat preference of Suter’s skinks (i.e. boulder beaches) provides some protection from rats, as the lizards can readily escape into narrow crevices. In this way, they also survived on Lady Alice, Whatupuke and Coppermine Islands (along with Wareware, Muriwhenua and Middle Stack), and have become abundant on all three islands following kiore eradication.
The only lizard seen under forest on Taranga was the ornate skink (Oligosoma ornatum), with nine seen foraging among leaf litter during the day – an encounter rate of just over one animal per day. Elsewhere in the group, ornate skinks also survived the presence of kiore on Lady Alice and Mauitaha Islands. Unlike most of the lizard species found in the Hen & Chickens group, ornate skinks remain widespread (though scarce) on the North Island mainland, from North Cape to Wellington.
The commonest reptile seen on Taranga was the moko skink (Oligosoma moco), with about 20 animals seen among sunlit low vegetation at all altitudes. Moko skinks have also been recorded on most of the islands in the Chickens group, including all five that had or have kiore present.
The seventh reptile species recorded from Taranga is the shore skink (Oligosoma smithi). The boulder beaches along the south coast of the island provide an abundance of suitable habitat, and I was surprised not to see any shore skinks despite considerable searching. They have been recorded from all islands in the group.
Four further lizard species have been recorded from the archipelago, with all four being confined to islands lacking kiore (prior to translocations of two species to three islands cleared of rats). Within the Chicken islands, Towns’ skink (a nocturnal, forest-dwelling species) was confined to Wareware, Muriwhenua, Pupuha and Middle Stack, before being translocated to Lady Alice Island in 1997 & 2005 (from Muriwhenua), Whatupuke in 2000 (from Middle Stack), and Coppermine Island in 2002 (from Middle Stack).
McGregor’s skink (a large, nocturnal species) has a relictual distribution on three islands off Northland – Sail Rock (south of Taranga), Bream Islands (off Whangarei Heads), and an island in the Cavalli Islands – plus Mana Island off the Wellington coast. From Sail Rock they were translocated to Lady Alice Island in 1997 and Whatupuke in 2000.
The two remaining lizard species (common gecko Woodworthia maculata and copper skink Oligosoma aeneum) both occur alongside introduced predators at many sites throughout the North Island and its offshore islands, but have curiously confined distributions within the Hen & Chickens Islands. This may be due to a combination of competition from related species (Pacific gecko and ornate skink respectively) as well as rat predation. The common gecko has been recorded from Sail Rock, Wareware and Muriwhenua, and the copper skink from Whatupuke, Lady Alice and Coppermine Islands.
McGregor’s skink, Towns’ skink, copper skink and common gecko are all candidate species for translocation to Taranga following the successful eradication of kiore there in May 2011.
With thanks to the Department of Conservation, Whangarei Field Centre, for logistic support and permission to visit Taranga, and Warren Farrelly for field assistance.
Related blogs
Taranga / Hen Island – 1933 and 2010 – In the footsteps of Edgar Stead (Part 1)
Reptiles of the Poor Knights Islands
A gift of lizards – 35 years to completion
Take that you dirty rat! – the unglamorous side of museum work