Oligosoma inconspicuum

Cryptic skink

Oligosoma inconspicuum
(Patterson & Dougherty, 1990)

Cryptic skinks. <a href="https://www.instagram.com/samanimalman/">© Samuel Purdie</a> (upper and lower), <a href="https://www.instagram.com/tim.harker.95/">© Tim Harker</a> (centre).
Image attribution
Cryptic skinks. © Samuel Purdie (upper and lower), © Tim Harker (centre).
Herpetofaunal category
NZ Skinks
Species complex
Conservation Status
At Risk - Declining
Common names
Cryptic skink

Length: SVL up to 75mm, with the tail being equal to or longer than the body length

Weight: up to 6 grams

Description

A beautifully patterned skink comprising a variety of geographic forms. Some of the forms in the complex may represent variation within a single species. However, some forms possess distinct morphological features, unique genetics, and occupy different niches/ are geographically separated. Consequently, it is probable that some of these geographic forms represent unique species, which are yet to be formally described. There is some debate, however, as to whether these are in fact, unique species (Chapple et al. 2011; Patterson 2011).

Cryptic skink: Mid to dark brown dorsal surface uniform or speckled with pale or dark flecks. Typically has a dark mid-dorsal stripe. Lateral surfaces bear a vivid dark lateral band, which is typically bordered with a pale-cream notched or smooth dorsolateral stripe. Chin and throat grey or yellowish, sometimes flecked with black. 60-75 mm SVL.

Oteake skink: Chestnut brown dorsal surface often with dark/black flecks and brown scales often enclosed by black margins. Mid dorsal stripe typically absent or very faint. Lateral surfaces bear a notched, thin, dull light brown and indistinct dorsolateral stripe with a dark lateral band. 60-70 mm SVL. Ventral surface yet to be recorded in live specimen. Soles of feet black. Eye color pale grey-green become blackish behind pupil. 

Big Bay skink: Chestnut to dark brown dorsal surface with bold black or dark brown mid dorsal stripe. Thick and distinctive dark mid dorsal stripe. Lateral surfaces typically bear a thick dark lateral band bordered by a pale cream lateral stripe and mid lateral stripe. Ventral surface with copper brown or yellow-brown belly and grey throat with black speckles. Tail keeled (i.e. raised scales). Eye color brownish. 18-20 subdigital lamellae. Soles of feet yellow-brown. 

Mahogany skink: Warm chestnut to dark brown uniform dorsal surface sometimes with dark flecks or rudimentary stripes. Mid dorsal stripe dull black sometimes indistinct. Thin, dull light brown and highly indistinct dorsolateral stripes. Lateral surfaces bear a dull mid-lateral stripe. Ventral surface with deep yellow belly, grey throat with moderate to bold black flecking. Tail keeled (i.e. raised scales) Eye colour pale green-grey. Subdigital lamellae 20-23. Soles of feet black. 

Humboldt skink: A large member of the cryptic skink complex with an SVL up to 80 mm. Mid to dark brown with a faintly marked back (few flecks and indistinct mid-dorsal stripe). Lateral surfaces with a dark band bordered by indistinct pale notched dorsolateral and mid lateral stripes. Ventral surface yellow with a uniform grey throat. 

Pallid skink: Dorsal surface light chestnut brown, dark brown, or grey-brown with scattered spots, blotches and broken stripes. Dark flecking on top of head. Lateral surfaces bear dull, clearly notched dorsolateral and mid-lateral stripes. Ventral surface creamy-grey, sometimes lightly mottled or strongly blotched with pale and dark flecks.

Herbfield skink: Dorsal surface glossy brown with dark mid-dorsal stripe. Lateral surfaces typically bear relatively smooth and bright pale cream dorsolateral and mid-lateral stripes. Ventral surface pale to yellowish, similar to cryptic skink. 

(Jewell 2019; Jewell 2008)

Life expectancy

Unknown.

Distribution

Cryptic skink: Found in the lowlands around Lake Wakatipu, Eyre Mountains, Thompson Mountains, Livingstone Mountains, Southland, Raratoka and Pig Islands in Foveaux Strait.

Oteake skink: Only known from a slither of habitat near Mt Kyeburn in Oteake Conservation Park, North Otago.

Big Bay skink: Known from northern Fiordland and South Westland from Big Bay to Barn Bay and the Cascade Plateau. Could possibly be a lowland specialist, as no confirmed sightings have occurred in alpine/subalpine habitat.

Mahogany skink: Known only from the Llawrenny Peaks in Fiordland (Transit Gully, Sinbad Gully, Mitre Peak).

Humboldt skink: Lake Wakatipu to adjacent Fiordland  peaks such as Mt Earnslaw, Humboldt Mountains, and Earl Mountains. 

Pallid skink: Currently known from Mt Cardrona, Coronet Peak, Hector Mountains, Garvie Mountains and Mataura Range. 

Herbfield skink: Known from lowland habitat in the Southland Plains (incl. Tiwai Point wetlands), Eastern Otago from the Aparima River to the Shag River. Can be found in the Dunedin area, Macraes Flat, and Wairio. 

Ecology and habitat

Cryptic skinks may differ in habitat use and ecology depending on geographic form, however, their habitat use and behavior is ultimately somewhat similar. These skinks are diurnal and terrestrial (occasionally semi-arboreal climbing into tall shrubs). While they do sun bask, they typically do so in a cryptic manner, while hiding in dense vegetation or near the entrance to their stone retreats. Consequently, they can sometimes be difficult to observe basking. These skinks have been recorded in a variety of habitats from the lowland right up to at least 1825 m (a.s.l). They exist in habitats such as tussocklands, grasslands, scrublands, herbfields, wetlands, and rocky areas (e.g. rocky beaches, shrubland, screes, tallus, vertical rock walls)(van Winkel et al. 2018).

Social structure

Laregly unknown. However, some have been seen in remarkably high densities (such as herbfield skinks), while others appear to be more solitary, or are lower in density (such as Oteake skinks and mahogany skinks).

Breeding biology

Poorly understood. Females produce 1-3 young annually (at least in lowland areas) in summer (January-March).

Diet

Cryptic skinks feed on small invertebrates and on the fruits of native shrubs, and the nectar of flowers.

Disease

Unknown. 

Conservation strategy

This species is not being actively managed, but taxonomic and genetic work is currently underway which will help to inform and protect populations that may be distinct species in their own right. Three populations of cryptic skink exist on predator-free Islands (Centre Island, Pig Island in Foveaux Strait and Tree Island in Lake Wakatipu), and at least one population of herbfield skinks exist in a predator-resistant environment (Ōrokonui Ecosanctuary, Dunedin). Additionally, surveys for poorly known forms such as Oteake skink are being conducted to try learn more about the distribution of this potentially threatened species. 

 

References

Chapple, D. G., Bell, T. P., Chapple, S. N., Miller, K. A., Daugherty, C. H., & Patterson, G. B. (2011). Phylogeography and taxonomic revision of the New Zealand cryptic skink (Oligosoma inconspicuum; Reptilia: Scincidae) species complex. Zootaxa2782(1), 1-33.

Jewell, T. (2019). Skinks of southern New Zealand. A field guide. Edition 4. 

Jewell, T. (2008). A photographic guide to reptiles and amphibians of New Zealand. Auckland: New Holland.

Patterson, G. B. (2011). Phylogeography and taxonomic revision of the New Zealand cryptic skink (Oligosoma inconspicuum; Reptilia: Scincidae) species complex.

van Winkel, D., Baling, M., Hitchmough, R. 2018. Reptiles and amphibians of New Zealand – a field guide. Auckland university press, Auckland New Zealand.