The South Island robin (Petroica australis; also known in Māori as the kakaruwai)[2] is a sparrow-sized bird found only in New Zealand, where it has the status of a protected endemic species.

P. traversi seems to be a Chatham Island derivative of P. australis, although the position of the most recent common ancestor has yet to be determined.

[5] The fossil record also indicates the robins' presence throughout lowland New Zealand until drastic habitat reduction through deforestation by the Polynesian ancestors of the Māori and later European colonisers.

[7] However, male North Island robins are almost black with a white spot just above the beak, as well as the greyish-white lower breast.

[1] It has fared slightly better than the Stewart Island robin, which has been relegated to 3 subpopulations, all of which are in Leptospermum swamp scrubland—although this is not their preferred habitat, it is less heavily populated by mammalian predators.

[6] When the population was introduced to Ulva Island, nesting was positively correlated with the presence of broad-leaved coastal vegetation.

They begin their breeding season fairly early in August or September (Southern Hemisphere spring) and thus can make use of the winter's remaining food stores during this time.

[16] Replacement clutches, in the case of loss of eggs or nestlings to predation, can be produced relatively rapidly, within 3–10 days.

[7] Invertebrates, including earthworms, beetles, and other arthropods foraged from the leaf litter comprise most of the South Island robins' diet.

South Island robins have a very good memory of their storage sites; a male was observed to empty as many as five consecutive caches before returning the stores to his mate during incubation.

[14] The birds have demonstrated an ability to differentiate and prioritise caches of varying sizes, up to 12 total items, without any training, which appears to be the highest recorded numerical competency of any wild animal.

[5] A male's call during non-breeding season is a series of loud notes with descending frequency, which start in rapid succession and finish slowly.

A side-effect of this behaviour might be the showcasing of a particular male's ability to sequester resources: the longer he sings, the more capable he is of finding food, and thus a better candidate for a mate.

[1] However, the Stewart Island robin (Petroica australis rakiura) has gone through a couple of bottlenecked populations recently because of deforestation and habitat loss, as well as introduced predators, such as rats, stoats, and feral cats.