Oligosoma alani

Robust skink

Oligosoma alani
(Robb, 1970)

Robust skink (Northland). <a href="https://www.instagram.com/nickharker.nz/">© Nick Harker</a>
Image attribution
Robust skink (Northland). © Nick Harker
Herpetofaunal category
NZ Skinks
Species complex
Conservation Status
At Risk - Recovering
Previous scientific names
Cyclodina alani
Common names
Robust skink

Length: SVL up to 158mm, with the tail being equal to or shorter than the body length

Weight: 105 grams

Description

New Zealand's largest native skink, reaching up to 33cm in total length. Robust skinks are large and thickset, with short limbs and toes (northern individuals of the species are particularly robust).

Dorsal (upper) surface mid to dark brown or pinkish brown with a series of irregular large blotches. Blotches are usually pale cream to yellow/brown, sometimes with a dark brown edge. Flanks are light grey to grey brown with blotches of a similar appearance to those on the back, Some individuals also have black and white markings above the shoulders. Belly colour ranges from yellow to a vivid reddish pink, sometimes with dark flecks. Throat cream, often with dark flecks. A yellow, black edged ‘tear drop’ is present below each eye. Robust skink have blunt snouts and large dark eyes. The base of the tail is very thick and tapers abruptly.

Life expectancy

Over 33 years (Mike Chillingworth personal communuication, 2019).

Distribution

Once widespread throughout the North Island, robust skinks only survived on islands which have never had introduced mammals. They are now confined to a few islands from the Coromandel to Aupouri Peninsula.

Robust skink sub-fossils have been recorded across the North Island including Northland, Motutapu Island near Auckland, Waitomo in the Waikato region, as well as Masterton and Mana Island near Wellington.

Ecology and habitat

Robust skinks are a strictly nocturnal species which emerges at dusk to forage, although gravid females have been known to sun-bask during the day. They will forage in the open at night and rely on crypsis / camouflage to avoid predation, but quickly retreat to cover or into deep leaf litter when disturbed.

Robust skinks are vulnerable to water loss through the skin so prefer areas of higher humidity which are thermally stable. During the day robust skinks inhabit thick leaf litter, or hide under rocks, logs, and seabird burrows in low coastal forest. They have also been found inhabiting native iceplant (Disphyma australe) and umbrella sedge (Cyperus ustulatus) in more open areas.

Social structure

Largely unknown, but considered to be solitary and territorial.

Breeding biology

Female robust skinks breed biennially (once every two years), and give birth to litters of up to seven young in May/June, with timing variable depending on weather/seasonal conditions (D. Keall, personal communication, October 6, 2016).

Diet

Robust skinks are primarily insectivorous, predating a wide range of invertebrates including insects and crustaceans. They are also frugivorous, consuming the fruits and berries from plants such as Kawakawa (Piper excelsum) and nightshade (Solanum spp.). At certain times of year fruit comprises around 30% of robust skinks' diet. They have also been recorded consuming smaller lizards, and diving petrel chicks.

Disease

Largely unknown. Have been reported with ecto-parasitic mites in the wild.

Conservation strategy

Robust skinks have been translocated to four additional pest free islands; Korapuki Island, Red Mercury and Stanley Island off the Coromandel Peninsula, and Motuopao Island near Cape Reinga in Northland.

Robust skink are classified by DOC as ‘recovering’. DOC have a recovery plan in place for the species, click here to read more.

Interesting notes

Robust skinks are New Zealand's largest native skink.

Because of their large size and nocturnal habits, robust skinks are particularly vulnerable to introduced mammalian predators, and would have been among the first lizard species to disappear from the mainland following the arrival of humans in New Zealand.

Robust skinks are genetically and morphologically distinct in the southern (Coromandel) and northern (Northland) parts of their range. These two sub-populations may be described as separate species in future.

References

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 Evolution, 52(2), 470-487.

Gill, B.J., & Whitaker, A.H. (2007). New Zealand frogs and reptiles. Auckland: David Bateman Limited.

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.

Towns, D. (1992). Recovery plan for Whitaker's skink and robust skink. Retrieved October 18, 2016 from http://www.doc.govt.nz/Documents/science-and-technical/TSRP03.pdf

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