Oligosoma aff. polychroma Clade 5
Southern grass skink
Oligosoma aff. polychroma Clade 5
Length: SVL up to 80mm, with the tail being equal to or slightly longer than the body length
Weight: unknown
Description
A very sleek and variable species of grass skink with a snout-vent-length (SVL) up to 80 mm. Southern grass skinks are often characterised by their dark to tan-brown dorsal (upper) surfaces, which may or may not exhibit a dark mid-dorsal stripe extending down the tail. Pale dorsolateral stripes (smooth or notched) are also present along their flanks. Their lateral surfaces (sides) are dominated by a dark brown lateral band with smooth or notched borders that are usually pale. The ventral (lower) surfaces are variable, but are often a uniform grey, brown, tan-brown, cream, white or yellow, with the throat often being lighter in colouration ranging from white-grey to grey-brown. Their eye colour is typically brown-tan but may have green hues. Hypermelanstic/dark individuals have been observed from some localities.
Southern grass skinks are difficult to differentiate from other members of the grass skink complex, however, Jewell (2022) notes that they can be differentiated from the tussock skink (Oligosoma chionochloescens) by their head shape (blunt snout vs. long snout), and by colour/pattern (at least at their contact zone), with the tussock skink being a lighter tan-brown, having smooth-edged stripes, and exhibiting complete mid-dorsal, and outer-dorsal stripes.
Life expectancy
Largely unknown, but as with most of Aotearoa's small endemic skinks, their life expectancy is likely to be at least 10-20 years in the wild.
Distribution
The southern grass skink is restricted to the Canterbury and Otago regions, reaching its northern limits around Banks Peninsula and Lake Tekapo, and being bounded to the south by Lake Wakatipu, the northern Crown Range, Pisa Range, Lindis Pass, St Bathans Range, Hawkdun and Ida Ranges, Danseys Pass, and the Kakanui Hills.
Ecology and habitat
Southern grass skinks are a very frequently seen species because they are diurnal, avid sun-baskers, and terrestrial. This species has been recorded in densities as high as 4000 per hectare (Wilson et al. 2017). Southern grass skinks inhabit a range of habitats including coastal dune habitat, wetlands, grassland, shrublands, rocky shrubland/herbfield, screes, tussock, stony river beds and even cities.
Social structure
Unknown.
Breeding biology
This species reproduces annually and is mature at about 3 years old. Mating likely takes place around March, with 3-6 offspring born in the summer months (November-February) (van Winkel et al. 2018).
Diet
Southern grass skinks are primarily insectivorous, feeding on small arachnids, beetles, and other invertebrates, but are also known to take advantage of the fruit and nectar of certain native plants when they are in season.
Disease
Southern grass skinks are known hosts for the ectoparasitic mites Odontacarus lygosomae, and Ophionyssus scincorum, as well as the blood parasite Hepatozoon lygosomarum.
They are known hosts for the trematode Dolichosaccus leiolopismae, a species seemingly restricted to Aotearoa's reptile fauna (Allison & Blair, 1987).
Conservation strategy
Listed in the most recent threat classification as 'At Risk - Declining'. This species is not being actively managed. However, when land is developed/destroyed, this species is often salvaged and relocated to suitable habitat. This species is also present at a number of predator-resistant sanctuaries.
Interesting notes
This species has been observed occupying insect burrows.
Southern grass skinks are members of a cryptic species complex which includes the northern grass skink (Oligosoma polychroma), Waiharakeke grass skink (Oligosoma aff. polychroma Clade 2), south Marlborough grass skink (Oligosoma aff. polychroma Clade 3), Canterbury grass skink (Oligosoma aff. polychroma Clade 4), and Tussock skink (Oligosoma chionochloescens). The various species are regionally distributed, similar in both appearance and habit, and were once regarded as a single highly variable species - the 'common skink'. There are currently no known morphological features to distinguish Southern grass skinks from the other species within the complex.
References
Jewell, T. (2008). A photographic guide to reptiles and amphibians of New Zealand. Auckland: New Holland.
Jewell, T. (2022). Discovery of an abrupt contact zone supports recognition of a new species of grass skink in southern New Zealand. Jewell Publications, Occasional Publication #2022B.
van Winkel, D., Baling, M., Hitchmough, R. 2018. Reptiles and amphibians of New Zealand – a field guide. Auckland university press, Auckland New Zealand.
Southern grass skink basking in coastal vegetation (Christchurch). © Nick Harker
