Robust skink (Oligosoma alani)

Synonyms: Cyclodina alani
GenusOligosoma (1)
SizeLength: c. 25 cm (2)
Weightc. 60 g (2)

Classified as Vulnerable (VU) on the IUCN Red List 2007 (3).

A relatively large New Zealand skink, the robust skink has, as its names suggests, a rather thickset body with a short, blunt head (2). The back is brown and patterned with irregular large, pale blotches with dark edges. The sides of the body are yellowish-grey with dark markings above the forelimbs, and the underside is yellowish (4). Beneath each conspicuously large eye sits a yellow tear-drop shaped marking, edged with black (2) (4). The limbs and toes of the robust skink are short and stumpy and the tail is thick at the base, but tapers abruptly (4). Previously classified within the genus Cyclodina, recent molecular evidence suggests that the robust skink, together with all native New Zealand skinks, should be placed within a single genus, Oligosoma (1).

In the past, the robust skink was found throughout much of the North Island, New Zealand and on many offshore islands. Today, natural populations of this lizard are found on just six small islands around the northern North Island: Matapia Island, Moturoa Island, Tatapihi (Groper) Island, Middle Island, Green Island and Castle Island. The largest of these islands, Middle Island, measures just 13 hectares in area. Robust skink populations have also been translocated to Korapuki Island, Stanley Island, Red Mercury Island and Motuopao Island (5).

The robust skink can be found under rocks, tree stumps, fallen logs or in seabird burrows, in areas where there is a dense cover of vegetation and much leaf litter (5). Robust skinks can lose a lot of water through their skin and so they generally inhabit damp environments in order to minimize this loss (5).

The robust skink is a nocturnal animal (5), which is known to feed on fruits (6), although like most other skinks, it probably also feeds on arthropods (7). During certain times of the year, fruit comprises around a third of the diet and as the seeds pass through undamaged, the skink may play a role in dispersing the seeds of some of New Zealand’s flora (6).

Once widespread on the mainland, and now only found on islands free of all introduced mammalian predators, the robust skink was probably lost from the mainland soon after Pacific rats (Rattus exulans) arrived around 1,000 years ago (5) (8). This highlights how exceptionally vulnerable the robust skink is to predation (2) and shows that the greatest threat facing the robust skink today is the possibility of a predator (a rodent, cat or mustelid) being introduced to the islands on which it occurs (2).

The robust skink has been the focus of a significant amount of conservation action. Two recovery plans have been published for this species; the first in 1992 laid out a five-year plan, while the second, made in 2002, set out objectives for the next ten years in order to build on the conservation work undertaken as part of the first plan (5).

As a result of these plans, rodents were removed from islands with suitable habitat for the robust skink, and skinks were then translocated to the now predator-free islands, establishing four new skink populations (5). Of the six small islands where natural populations of robust skinks occur, three are reserves where access can be controlled and another is protected by its extreme inaccessibility (5). This offers the robust skink some protection from the introduction of a predator to the islands, which could potentially have devastating consequences for this vulnerable reptile.

For further information on conservation of the robust skink see:

Authenticated (29/04/09) by Dr David Towns, New Zealand Department of Conservation.

  1. IUCN Red List (December, 2009)