Oligosoma polychroma

Northern grass skink

Oligosoma polychroma
(Patterson & Daugherty, 1990)

Northern grass skinks. <a href="https://www.instagram.com/nickharker.nz/">© Nick Harker</a> (above), <a href="https://www.instagram.com/samanimalman/">© Samuel Purdie</a> (below).
Image attribution
Northern grass skinks. © Nick Harker (above), © Samuel Purdie (below).
Herpetofaunal category
NZ Skinks
Species complex
Conservation Status
Not Threatened
Previous scientific names
Oligosoma nigriplantare polychroma,
Lygosoma moco
Common names
Northern grass skink,
Common skink.

Length: SVL up to 80mm, with the tail being equal to or slightly longer than the body length

Weight: Up to at least 5 grams

Description

Formerly known as the 'common skink', northern grass skinks are an abundant species that is commonly encountered in both native and modified habitats such as suburban gardens.

Head has a short, blunt snout. Pattern can be highly variable. The dorsal surfaces are often various shades of brown with cream or pale-brown dorsolateral stripes which may be smooth-edged or serrated, a mid dorsal stripe (when present) usually extends down the tail. Flanks have a broad dark brown lateral stripe, often edged with black and bordered below by a cream-coloured stripe which may be smooth or crenulated. A pale stripe runs down the anterior surface of the forelimb. The ventral surface is variously coloured shades of grey, brown, or yellow, without speckling. 

Life expectancy

Northern grass skinks have been reported living up to four years in the wild, and up to six years in captivity.

Distribution

Occurs from the central North Island to Wellington in the North Island, and from Nelson along the West Coast to Hokitika in the South Island. In the northern South Island, the species eastern extent is Takapourewa / Stephen's Island in the western Marlborough Sounds, further east it is replaced by a related species - the Waiharakeke grass skink (Oligosoma aff. polychroma Clade 2). Further south it is replaced by the South Marlborough grass skink (Oligosoma aff. polychroma Clade 3) and Canterbury grass skink (Oligosoma aff. polychroma Clade 4) to the east and south of it's range.

Ecology and habitat

Northern grass skinks are diurnal, bold and strongly heliothermic. They can often be seen out basking fully exposed in sunny areas.

In common with other grass skinks the species occupies a wide range of habitat types preferring open areas including coastal vegetation, rock piles, grassland, flaxland, shrubland, screes, forest margins tussock and modified urban / suburban habitats. Often takes refuge in dense vegetation or under rocks and logs when not active.

Social structure

Thought to be largely solitary, but often lives in high-density colonies where multiple individuals can be observed basking in close proximity.

Breeding biology

Northern grass skinks reach maturity in around two years, mating has been reported to occur in March, and females reproduce annually giving birth to litters of up to six juveniles in mid-to-late summer (January- February).

Diet

Northern grass skinks are active hunters and consume a wide range of small invertebrates such as spiders, insects, isopods and molluscs. They also consume the berries / fruit from native plants.

Disease

Northern grass skinks are known hosts for the ectoparasitic mites Neotrombicula sphenodonti, Odontacarus lygosomae, and Ophionyssus scincorum, as well as endoparasitic nematodes in the Skrjabinodon genus. The malaria Plasmodium lygosomae is also known from this species.

Conservation strategy

Northern grass skinks are regarded as "Not Threatened" having a wide distribution and generally occurring in abundance at sites throughout its range.

No specific conservation strategy has been developed for Northern grass skinks although they do occur on several pest-free islands.

Interesting notes

Northern grass skinks are members of a cryptic species complex which includes the 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 southern grass skink (Oligosoma aff. polychroma Clade 5). 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 northern grass skinks from the other species within the complex.

References

Carpenter, J. K., Monks, J. M., & Nelson, N. (2016). The effect of two glyphosate formulations on a small, diurnal lizard (Oligosoma polychroma). Ecotoxicology25(3), 548-554.

Chapple, D. G., Ritchie, P. A., & Daugherty, C. H. (2009). Origin, diversification, and systematics of the New Zealand skink fauna (Reptilia: Scincidae). Molecular phylogenetics and evolution52(2), 470-487.

Cree, A. (1994). Low annual reproductive output in female reptiles from New Zealand. New Zealand journal of zoology21(4), 351-372.

Daugherty, C. H., Patterson, G. B., Thorn, C. J., & French, D. C. (1990). Differentiation of the members of the New Zealand Leiolopisma nigriplantare species complex (Lacertilia: Scincidae). Herpetological monographs, 61-76.

Dent, E. (2016) The impacts of an introduced mammalian predator (Mus musculus) on tree weta (Hemideina trewicki) and skinks (Oligosoma polychromaOligosoma infrapunctatum and Oligosoma lineoocellatum) in Cape Sanctuary, Hawkes Bay. Unpublished MS thesis, Victoria University of Wellington, Wellington, 84 pp.

East, K. T., East, M. R., & Daugherty, C. H. (1995). Ecological restoration and habitat relationships of reptiles on Stephens Island, New Zealand. New Zealand Journal of Zoology22(3), 249-261.

Gill, B. J. (1976). Aspects of the ecology, morphology, and taxonomy of two skinks (Reptilia: Lacertilia) in the coastal Manawatu area of New Zealand. New Zealand journal of zoology3(2), 141-157.

Gollin, J. F., Gorman, N., & Armstrong, D. P. (2021). Twenty years on. New Zealand Journal of Ecology45(1), 1-9.

Hardy, G. S. (1977). The New Zealand Scincidae (Reptilia: Lacertilia); a taxonomic and zoogeographic study. New Zealand journal of zoology4(3), 221-325.

Hare, K. M., Pledger, S., Thompson, M. B., Miller, J. H., & Daugherty, C. H. (2006). Daily patterns of metabolic rate among New Zealand lizards (Reptilia: Lacertilia: Diplodactylidae and Scincidae). Physiological and Biochemical Zoology79(4), 745-753.

Hitchmough, R., Barr, B., Knox, C., Lettink, M., Monks, J. M., Patterson, G. B., Reardon, J. T., van Winkel, D., Rolfe, J., & Michel, P. (2021). Conservation status of New Zealand reptiles, 2021New Zealand threat classification series 35. Wellington: New Zealand Department of Conversation.

Hitchmough, R.A., Barr, B., Lettink, M., Monks, J., Reardon, J., Tocher, M., van Winkel, D., Rolfe, J. (2016). Conservation status of New Zealand reptiles, 2015; New Zealand threat classification series 17. Wellington: New Zealand Department of Conservation.

Jewell, T. (2011). A photographic guide to reptiles and amphibians of New Zealand. Auckland: New Holland Publishing.

Laird, M. (1951). Plasmodium lygosomae n. sp., a parasite of a New Zealand skink, Lygosoma moco (Gray, 1839). The Journal of Parasitology37(2), 183-189.

Liggins, L., Chapple, D. G., Daugherty, C. H., & Ritchie, P. A. (2008). A SINE of restricted gene flow across the Alpine Fault: phylogeography of the New Zealand common skink (Oligosoma nigriplantare polychroma). Molecular Ecology17(16), 3668-3683.

Middleton, D. M., La Flamme, A. C., Gartrell, B. D., & Nelson, N. J. (2014). Reptile reservoirs and seasonal variation in the environmental presence of Salmonella in an island ecosystem, Stephens Island, New Zealand. Journal of wildlife diseases50(3), 655-659.

Middleton, D. M., Minot, E. O., & Gartrell, B. D. (2010). Salmonella enterica serovars in lizards of New Zealand's offshore islands. New Zealand Journal of Ecology, 247-252.

Mockett, S. (2017). A review of the parasitic mites of New Zealand skinks and geckos with new host records. New Zealand journal of zoology44(1), 39-48.

Mockett, S., Bell, T., Poulin, R., & Jorge, F. (2017). The diversity and evolution of nematodes (Pharyngodonidae) infecting New Zealand lizards. Parasitology144(5), 680-691.

O’Donnell, C. F., Weston, K. A., & Monks, J. M. (2017). Impacts of introduced mammalian predators on New Zealand’s alpine fauna. New Zealand Journal of Ecology41(1), 1-22.

Patterson, G. B., & Daugherty, C. H. (1990). Four new species and one new subspecies of skinks, genus Leiolopisma (Reptilia: Lacertilia: Scincidae) from New Zealand. Journal of the Royal Society of New Zealand20(1), 65-84.

Patterson, G. B., & Daugherty, C. H. (1995). Reinstatement of the genus Oligosoma (Reptilia: Lacertilia: Scincidae). Journal of the Royal Society of New Zealand25(3), 327-331.

Robb, J. (1986). New Zealand Amphibians & Reptiles (Revised). Auckland: Collins, 128 pp.

Spencer, N. J., Thomas, B. W., Mason, R. F., & Dugdale, J. S. (1998). Diet and life history variation in the sympatric lizards Oligosoma nigriplantare polychroma and Oligosoma lineoocellatumNew Zealand journal of zoology25(4), 457-463.

Towns, D. R., & Elliott, G. P. (1996). Effects of habitat structure on distribution and abundance of lizards at Pukerua Bay, Wellington, New Zealand. New Zealand journal of ecology, 191-206.

Towns, D. R., Neilson, K. A., & Whitaker, A.H. (2002). North Island Oligosoma spp. skink recovery plan 2002–2012: Threatened species recovery plan 48. Wellington: Department of Conservation.

van Winkel, D., Baling, M. & Hitchmough, R. (2018). Reptiles and Amphibians of New Zealand: A field guide. Auckland: Auckland University Press, 376 pp.

Whitaker, A. H. (1987). The roles of lizards in New Zealand plant reproductive strategies. New Zealand journal of botany25(2), 315-328.

Wotton, D. M., Drake, D. R., Powlesland, R. G., & Ladley, J. J. (2016). The role of lizards as seed dispersers in New Zealand. Journal of the Royal Society of New Zealand46(1), 40-65.