Oligosoma waimatense

Scree skink

Oligosoma waimatense
(McCann, 1955)

Scree skink (Wairau, Marlborough). <a href="https://www.instagram.com/nickharker.nz/">© Nick Harker</a>
Image attribution
Scree skink (Wairau, Marlborough). © Nick Harker
Herpetofaunal category
NZ Skinks
Species complex
Conservation Status
Threatened - Nationally Vulnerable
Previous scientific names
Leiolopisma grande waimatense,
Girardiscincus waimatense,
Leiolopisma otagense form “waimatense”.
Common names
Scree skink

Length: SVL up to 114 mm, with the tail being much longer than the body length

Weight: Up to at least 28 grams

Description

A beautiful and highly active species of large skink with a snout-vent-length (SVL) up to 114 mm. There are three main forms of scree skink. The Marlborough form, the Canterbury form, and the Otago form. It is possible that some or all of these forms warrant separate species status (unpubl. data), however, formal taxonomic work is yet to be completed. Mitochondrial DNA analyses indicate that the Otago form has introgressed with Otago skinks (Oligosoma otagense) at some point in the past, thus, their distinctiveness is uncertain (unpubl. data). The three main forms can be characterized as follows:

Marlborough

Dorsal surface typically bright golden or tan (sometimes with olive-green tint) with pronounced black transverse bands and black edging to many of the scales around the mid-dorsal area. There is sometimes a conspicuous "gap" along the dorsolateral area, where bold black bands are absent. The lateral surfaces are similar to the dorsal surface, with bold black transverse bands extending most of the way to the ventral surface. However, the basal color of the mid-lower portion of the lateral surfaces quickly transition to a pale grey color. Ventral surface and throat mostly uniform grey sometimes with a pale pink hue to the belly. 

Canterbury

Dorsal surface typically drab pale or dark grey (sometimes with olive-green tint) with less pronounced black transverse bands and conspicuous dense speckles. In this form there is also sometimes a "gap" along the dorsolateral area, where black bands and dense speckles are absent. The lateral surfaces are similar to the dorsal surface, however the black bands are often absent. Instead, only dense black or brown speckles are present. In the Canterbury form, the transition from the dorsal basal colour to the ventral surface colour is less abrupt. Ventral surfaces similar to the lateral surfaces, but more uniform pale grey with few speckles and sometimes a pale orange hue.

Otago

Dorsal surface typically bright cream-yellow or tan (sometimes with olive-green tint), often with pronounced black transverse bands, and/or with black markings that protrude longitudinally. There is sometimes a series of conspicuous "gaps" along the dorsolateral area, where bold black bands periodically extend from the dorsal area to the lateral area. This results in what looks like a cream-yellow or tan dorsolateral stripe that is broken up or crenulated. Lateral surfaces similar to dorsal surfaces, with bold black bands or patterns, with a basal color that transitions to grey on the lower lateral surface. Ventral surfaces typically uniform pale grey with few speckles.

Life expectancy

Upper limit unknown. However, it is probable that this species can live over 20 years.

Distribution

Marlborough form

Upper Wairau River, Chalk Range, Clarence River, Inland Kaikōura Range, and Seaward Kaikōura Range.

Canterbury form

South-Mid Canterbury, Lake Benmore, Grampian Mountains, Dalgety Range, Two Thumb Range, Rangitata Gorge, Lake Heron, and like Coleridge.

Otago form

From Waitaki/lower Pukake southwards including the Dunstan Range, Ida Range and Saint Bathans Range in north Otago. May also have existed on Black Jacks Island in Lake Benmore. 

Ecology and habitat

Scree skinks are diurnal, saxicolous, and avidly heliothermic. They are renowned for being highly active and mobile, with a maximum recorded home range size of 950 metres squared (Lettink and Monks 2019). Scree skinks occur in both the lowlands and subalpine environments. They typically inhabit dry rocky areas with suitable refugia (their large size renders them more vulnerable to predators). These include boulderfields, screes, tallus, stoney river terraces and banks, rocky shrubland, and rocky bluffs. 

Social structure

Unknown. 

Breeding biology

Largely unknown, however, scree skinks may breed annually or biennially. Reproductive maturity is thought to be a minimum of 4-5 years of age (Lettink and Monks 2019).

Diet

Invertebrates, smaller lizards (possibly including conspecifics), and native fruits.

Disease

Unknown.

Conservation strategy

Scree skinks are highly vulnerable to mammalian predation, partly because of their large size. Consequently, they only exist in a few areas in lowland habitat (compared to what their former extent would likely have been), and are more common and widespread at higher altitudes. However, when considering the decline of other mainland lizard populations, including other scree skink populations, it is probable this species is declining as a whole (Lettink and Monks 2019). A decade-long study by Lettink and Monks (2009) indicated that severe flooding and weather events may be a serious threat to scree skink populations. Following a severe weather event, a decline of 84% was observed in one scree skink population. This population gradually recovered after approximately 8.5 years unmanaged (Lettink and Monks 2019).

The authors of this comprehensive study made several highly useful conservation recommendations. Firstly, they suggested that monitoring at their study site continue, as studying a flood-prone population of scree skinks is highly valuable in the context of climate change. They also suggested that other scree skink populations be monitored long-term (e.g. 10 years) in scree systems, as their study site is fairly atypical of the species usual habitat. They also recommended that wilding conifers and other exotic trees should be controlled at scree skink sites, as shading out of habitat is thought to be a possible threat to scree skinks (Whitaker 2008; ML unpbl. data).

Interesting notes

Scree skinks are closely related to Otago skinks (Oligosoma otagense). Wild scree skinks in the Otago area show introgression with Otago skinks, and Marlborough scree skinks have been known to inadvertently hybridise with Otago skinks in captive situations.

References

Lettink, M., & Monks, J. M. (2019). Ecology of scree skinks (Oligosoma waimatense) in O Tu Wharekai Wetland, mid-Canterbury high country, New Zealand. New Zealand Journal of Ecology43(1).

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

Whitaker T 2008. Conservation of lizards in Canterbury Conservancy. Canterbury Series 308. Christchurch, Department of Conservation.