South Island robin

The South Island robin (Petroica australis; also known in Māori as the ) is a sparrow-sized bird found only in New Zealand, where it has the status of a protected endemic species. The birds are sparsely distributed through the South Island and Stewart Island / Rakiura, although the distribution is not continuous. The nominate, and the Stewart Island robin (P. australis rakiura) are the two subspecies. The species is closely related to the North Island robin (formerly P. australis longipes, now considered a distinct species), and also to the extremely rare black robin (P. traversi) of the Chatham Islands.

Taxonomy

thumb|left|South Island robin

The South Island robin has two subspecies: P. australis australis, the nominate form, and P. australis rakiura, the Stewart Island robin. These subspecies do not overlap in their distributions. The North Island robin (P. longipes), the tomtit (Petroica macrocephala), and the black robin (Petroica traversi) in the Chatham Islands are closely related 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.

Fossil record

There is molecular phylogenetic evidence to suggest two waves of immigration by the Petroica genus from Australia. P. longipes and P. australis can be traced to the first and P. macrocephala to the second wave. The evidence suggests that P. longipes and P. australis began to diverge prior to the Pleistocene era, and that the two South Island subspecies of P. australis began to diverge after the Pleistocene era. The separation time for the former was about three million years, and only 10,000 years (i.e., postglacial) for the latter. Fossils of New Zealand robins can sometimes be found near pit fall deposits, as they do most of their feeding/foraging on the ground. 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.

Description

thumb|right|Stewart Island robin

The South Island robin is a small passerine, 10–18 cm in length and weighing around 35 g. North Island robins do resemble both females and juveniles of the South Island robins, as well as all the Stewart Island robins, which can sometimes make it difficult to distinguish between the three. The females and juveniles within a particular group of robins look similar to each other, although newly independent juveniles may not yet have the more lightly coloured breast patch. However, male North Island robins are almost black with a white spot just above the beak, as well as the greyish-white lower breast. Females and juveniles are greyer with more variable pale patches on their breasts and throats. Male South Island robins are dark grey, except for the distinct yellowish-white lower chest, while females and juveniles are again lighter grey with a less distinct breast. Finally, Stewart Island robins look similar to North Island robins (both males and females).

Distribution

thumb|right|South Island robin, [[Southland District]]

Historically, the South Island robin inhabited much of the lowland of New Zealand's South Island, but its distribution has become much more patchy in the last century due to habitat loss and introduced predation. There are two populations on the east coast of the South Island, and they are slightly more common in the north and west. A programme of translocation to predator-free islands (such as Ulva Island, Motuara Island, and Nukuwaiata Island) was instituted and proved relatively successful at establishing new populations (around 600 individuals on Motuara alone). In the South Island, P. australis has a strong affinity for Douglas fir plantations, instead of the native forests (kanuka trees) or Monterey pine plantations. This is apparently due to forest structure rather than strict food availability or viable nesting sites, as the species prefers structurally simple forests with dense, even canopies, and ground covered with leaf litter.

Behaviour and ecology

Breeding

South Island robins are genetically monogamous, and extra-pair paternity is rare. As they do typically remain monogamous, are non-migratory, and remain on their breeding territories year-round, a male and female in one territory will compete for food resources during non-breeding times. Competition is reduced somewhat by slightly different foraging methods; however, they will steal from their mate's cache if given the opportunity. During breeding season, the female is solely responsible for nest building and incubation, and the male will provide the female and the hatchlings with food. Replacement clutches, in the case of loss of eggs or nestlings to predation, can be produced relatively rapidly, within 3–10 days. 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. Because of its high metabolic rate, a robin might spend as much as 90% of its day foraging or storing during the winter.

Conservation

thumb|right|Banded South Island robin at [[:en:Orokonui Ecosanctuary|Orokonui Ecosanctuary]]

The South Island robin is listed as being of least concern on the IUCN Red List. A 2012 scientific study of a marked population by the University of Otago during a contemporary 1080 poison operation using cereal baits showed no negative impact on robins, and suggested a likely population increase by reducing predation pressure from introduced mammals. However, some robin deaths have been recorded as a result of accidental 1080 poisoning following pest control operations. Most of these were associated with four specific operations in the 1980s that used poor-quality carrot baits.

References

External links

New Zealand Robin on Department of Conservation website
Factsheet on toutouwai, the New Zealand robin at NZBirds.com
Information about New Zealand robins on Te Ara
Protocols for monitoring New Zealand robins(Petroica australis) – Department of Conservation Technical Series No. 13
Video footage of New Zealand robins on the Animal Health Board YouTube Channel