Oligosoma nigriplantare

Chatham's skink

Oligosoma nigriplantare
(Peter's, 1873)

Chatham's skink (Rangatira/South East Island). <a href="http://edinz.com/">© Edin Whitehead</a>
Image attribution
Chatham's skink (Rangatira/South East Island). © Edin Whitehead
Herpetofaunal category
NZ Skinks
Species complex
Conservation Status
At Risk - Relict
Previous scientific names
Oligosoma nigriplantare nigriplantare
Common names
Chatham's skink

Length: SVL up to 98mm, with the tail being longer than the body (up to 1.5x)

Weight: unknown

Description

This enigmatic skink is the sole representative of reptiles on the Chatham archipelago. It is a highly variable species bearing visual and genetic similarities to the grass skinks (Oligosoma polychroma & affiliated species) of the New Zealand mainland.

Their colouration ranges from golden/green-brown, through to dark brown or black (which is typical for populations on rock stacks), often exhibiting a notched dark brown stripe bordered by light brown running along their dorsolateral surface from the nostrils to the base of the tail where it begins to break up. A mid-dorsal stripe is often present, as well as flecking along the flanks and dorsal surfaces. Under surfaces often a uniform pale brown through to yellow-green.

Visually similar to the grass skinks of mainland New Zealand, but unlikely to be confused with them as they are geographically isolated, with Chatham’s skink being the only lizard species present on the Chatham Islands.

Life Expectancy

Unknown.

Distribution

The Chatham’s skink is restricted to the Chatham Islands, an island group sitting roughly 800 km east of New Zealand. Once occurring throughout the archipelago, this species is now only found on Pitt Island and its surrounding islands, as well as some of the more remote rock stacks including The Sisters, and The Pyramid. This species is extinct on the main Chatham Island.

Ecology and Habitat

A diurnal species, that occurs in a multitude of habitats including open grasslands, fernland, shrubland, open bush edges, as well as rocky platforms with minimal vegetation. The species is very conspicuous often being observed moving through habitat or openly basking on logs, low shrubs such as flax etc., as well as rocky platforms on the smaller islets of the archipelago.

Social Structure

Solitary, but often observed in large aggregations when basking, sometimes lying on top of others. Densities can be extremely high with estimates of around 10 individuals per square metre on some of the smaller rock stacks such as The Pyramid.

Breeding Biology

Viviparous (Live-bearing). Mating occurs in autumn, with up to 4 young born in late January-February.

Diet

As with most of our native skinks, this species is omnivorous feeding on both invertebrates (spiders, insects, and crustaceans), and soft fruits. Individuals and populations occurring around seabird colonies are also known to take advantage of regurgitated fish etc. that is left over after the feeding of chicks.  

Disease

Largely Unknown.

Conservation status

Fairly abundant on predator-free islands within the Chatham group. The major threats to this species are the plethora of mammalian pests that have been introduced to the Chatham group.

References

Liggins, L., Chapple, D. G., Daugherty, C. H., & Ritchie, P. A. (2008). Origin and post‐colonization evolution of the Chatham Islands skink (Oligosoma nigriplantare nigriplantare). Molecular Ecology17(14), 3290-3305.

van Winkel, D., Baling, M., & Hitchmough, R. (2018). Reptiles and Amphibians of New Zealand: A Field Guide. Auckland University Press, pp376.