Field of Science

The Australasian Not-Robins

I've complained in the past about the decided lack of imagination displayed by many British naturalists when describing the fauna of Australasia. So many animals got lumbered with the names of European species to which they bore a superficial resemblance but of which they were not necessarily close relatives. So we got warblers that are not warblers, cod that are not cod, and the subject of today's post: robins that are not robins.

Male scarlet robin Petroica boodang, copyright Patrick Kavanagh.


Petroica is a genus of small perching birds found widely in Australasia, including species on various islands of the south Pacific. They are dumpy little birds whose males often have contrasting colour patterns with a dark dorsum and a light underside, though a couple of species are uniformly black. A number of species have red patches on the forehead and/or breast, and it is not too difficult to see why British naturalists chose to compare them to the European robin. They are insectivores, gleaning prey from vegetation or on the ground.

Over a dozen species are recognised in the genus Petroica, though the exact number varies depending on the author. Phylogenetic studies indicate four main lineages within the genus (Kearns et al. 2018) with some correlation between phylogeny and distribution. An Australian clade includes the scarlet robin P. boodang, the flame robin P. phoenicea, the pink robin P. rodinogaster and the rose robin P. rosea. As is indicated by their names, these are all red- or pink-chested forms, and they are found in woodlands in southeastern and southwestern Australia where they usually feed from leaves and branches. Females are duller in coloration, mottled grey or brown above and having the red on the underside lessened or lost; for the most part, the same pattern applies to females of the species described below.

Red-capped robin Petroica goodenovii, copyright Patrick Kavanagh.


More arid parts of Australia are inhabited by the red-capped robin Petroica goodenovii which is more terrestrial in habits than the preceding species. The red-capped robin forms a clade with two insular species, the Norfolk Island robin P. multicolor and the Pacific robin P. pusilla, the latter being found over a wide range from the Solomon Islands to Samoa (with a subfossil record from Tonga). The Norfolk Island robin is endangered with only an estimated 400 to 500 pairs surviving, a position whose severity was not fully appreciated until recently owing to the Norfolk Island and Pacific robins previously being regarded as conspecific with the Australian scarlet robin (Kearns et al. 2016). Kearns et al. (2016, 2018) also identified a strong genetic divergence between Pacific robins from the Solomon Islands and the eastern part of their range, suggesting the possibility of a further species division. However, they did not support such a divergence for the Samoan population which had previously been suggested as a candidate species by plumage and song characters.

Snow mountain robin Petroica archboldi, copyright Papua Expeditions.


The third clade includes two montane New Guinean species, the subalpine robin Petroica bivittata and the snow mountain robin P. archboldi. The male subalpine robin has a black back and white breast, without any red patches, and the species is found in high mountain forests and shrublands. The snow mountain robin, on the other hand, is a large Petroica species that is mostly slate-grey in coloration with a small red patch on the upper breast. It is found at the highest altitude of any bird in New Guinea and is the only bird found there in rocky scree habitats above the tree line. Both the New Guinean Petroica species, but particularly P. archboldi, have disjointed, localised ranges, and Kearns et al. (2018) expressed concern about the snow mountain robin's likelihood of future survival in the face of mining pressures and temperature rises.

North Island robin Petroica longipes, copyright Tony Wills.


The fourth and final clade, albeit a weakly supported one, unites the New Zealand Petroica species. Historically, most authors have recognised three Petroica species in New Zealand that, with the typical pithiness often associated with discussions of the somewhat depauperate New Zealand fauna, were generally known simply as the robin P. australis, the black robin P. traversi, and the tomtit P. macrocephala. However, multiple subspecies have been recognised within both the robin and the tomtit and recent years have seen calls for all to be recognised as distinct species (potentially raising the number of species in New Zealand to nine). Acceptance of these proposals has been varied: the North Island robin P. longipes now seems to be generally accepted as a separate species from the South Island P. australis but I have seen less recognition of more than one species of tomtit. The New Zealand robins are largely terrestrial feeders, and are noticeably longer-legged than other Petroica species. Male New Zealand robins are also duller in coloration with brownish backs. The more arboreal tomtits are the more similar in overall appearance to Petroica species from elsewhere. Most tomtit males are black above and white or yellow below. For the most part, female tomtits resemble other Petroica species in being duller than the males, brown above rather than black, but the female Auckland Island tomtit P. (macrocephala) marrineri is closer in appearance to the male. The Snares Island tomtit P. (macrocephala) dannefaerdi is uniformly black in both sexes. In this it resembles the larger black robin of the Chatham Islands, some distance east of New Zealand's South Island. Black robins are most reknowned for their conservation history with introduced predators reducing the entire species' population to only five individuals in 1980, including only a single breeding female. An intensive management program was instituted beginning with the capture and transfer of the entire population to a predator-free island. Higher breeding rates were encouraged through the removal of egg clutches from robin nests, with the bereaved birds laying a new batch to replace them and the original clutch placed in a nest of the local tomtit race to be raised cuckoo-style. As a result of this effort, population numbers increased until the current black robin population numbers about 250 individuals. Obviously, that's by no means enough to count their survival assured (and questions still linger about what, if anything, will be the long-term effects of inbreeding from such a minute founding populations) but it's still one heck of a lot better than what it was.

REFERENCES

Kearns, A. M., L. Joseph, L. C. White, J. J. Austin, C. Baker, A. C. Driskell, J. F. Malloy & K. E. Omland. 2016. Norfolk Island robins are a distinct endangered species: ancient DNA unlocks surprising relationships and phenotypic discordance within the Australo-Pacific robins. Conserv. Genet. 17: 321–335.

Kearns, A. M., L. Joseph, A. Thierry, J. F. Malloy, M. N. Cortes-Rodriguez & K. E. Omland (in press 2018) Diversification of Petroica robins across the Australo-Pacific region: first insights into the phylogenetic affinities of New Guinea's highland robin species. Emu.

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