New Zealand Robin

New Zealand Robin
South Island Robin (Petroica australis australis)
Conservation status
Least Concern (IUCN 3.1)
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Aves
Order:	Passeriformes
Family:	Petroicidae
Genus:	Petroica
Species:	Petroica australis
Binomial name
Petroica australis Sparrman, 1788

The New Zealand Robin or Toutouwai (Māori), Petroica australis, 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 South Island and Stewart Island/Rakiura, although the distribution is not continuous. The South Island Robin (Petroica australis australis), and the Stewart Island Robin (Petroica australis rakiura) are today accepted as subspecies. The species is closely related to the North Island Robin (formerly Petroica australis longipes, now considered a distinct species ^[1]), and also to the extremely rare Black Robin (Petroica traversi) of the Chatham Islands.

Abstract

When using the name New Zealand Robin, one might be referring to any of three separate birds, depending on geographic location within New Zealand. On the North Island the New Zealand robin is (Petroica longipes), a completely different species from the other two subspecies. The South Island robin and the Stewart Island robin, (both still New Zealand robins) are (Petroica australis australis) and (Petroica australis rakiura), respectively. These two subspecies, although they could physically interbreed, are not given the opportunity to do so as they are geographically isolated from one another. All of the New Zealand robins look alike, with only small differences in appearance which differentiate the groups. These birds are endemic to New Zealand, and while they are not technically a threatened species, they have suffered from habitat losses and predation by introduced species because of human interactions with the birds’ native environment. Conservation is therefore aimed at protecting what is left of the (Petroica australis) habitat, and reintroducing populations to areas where the introduced predators have been eradicated.

Diagnosis

(P. australis) are small, 10-18cm, and weigh around 35g. 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, with the exception of its geographic location. The females and juveniles within a particular group of robins look similar to each other except newly independent juveniles may not yet have the more lightly colored breast patch. ^[2] However, North Island males are almost black with a white spot just above the beak as well as the grayish-white lower breast. Females and juveniles are grayer with more variable pale patches on their breasts and throats. The South Island males are dark gray except for the distinct yellowish white lower chest, while females and juveniles are again lighter gray with a less distinct breast. Finally, Stewart Island robins look similar to North Island robins (males and females). ^[3]

General Description and Taxonomy

In general, the male's plumage is a dark gray while the female is dark gray-brown. On both birds the throat and belly are considerably lighter, in the male a cream color, which, in comparison with the European Robin’s similarly bright chest, is why the New Zealand Robin is referred to as such. Usually they are found on the edges of the forest, and can often be found in the green belts of towns and cities. These birds are endemic to New Zealand. They are naturally tame and inquisitive toward humans and are therefore easily trained. ^[4]

(Petroica australis) is situated in the order Passeriformes of the class Aves within the phylum Chordata of the kingdom Animalia. (P. australis) has two subspecies, (P. australis australis) (South Island robin) and (P. australis rakiura) (Stewart Island robin). These two groups are subspecies because although they can interbreed, they do not inhabit the same geographic area, and thus do not have the opportunity to interbreed. On the other hand, the North Island robin, (Petroica longipes), is classified as a completely separate species because of the deep divergence between the mitochondrial DNA phylogeny of the two groups. The Petroicidae family to which all of these robins belong are Australo-Papuan robins of which there are 44 species in Australia, New Zealand, and New Guinea, and they are not closely related to either the North American robin (family Turdidae) nor the Eurasian robins (family Muscicapidae). They are closely tied genetically with the Black Robin ((Petroica traversi)) in the Chatham Islands and the tomtit ((Petroica macrocephala)). (P. traversi) seems to be a Chatham Island derivative of (P. australis). It has yet to be determined how close the most recent common ancestor is between (P. macrocephala) and (P. australis). ^[1])

Fossil Record

There is molecular phylogenetic evidence to suggest that two waves of immigration by the Petroica genus from Australia. The first wave produced (P. longipes) and (P. australis), while the second produced (P. macrocephala). Furthermore, the evidence suggests that the two species on the North and South (including Stewart) Islands of New Zealand began to diverge prior to the Pleistocene era and the two remaining species are the only ones to do so after the Pleistocene glacial cycles. The 5.9% sequence divergence between the North and South species in a certain part of their mitochondrial genomes indicates a separation time of about three million years. ^[1]) This is in contrast with the mere 10,000 year separation between (P. australis australis) and (P. australis rakiura) (since the last glaciation). Fossils for New Zealand robins can sometimes be found near pit fall deposits, as they do most of their feeding/foraging on the ground. ^[5] The fossil record also indicates the robins’ presence throughout lowland New Zealand until drastic habitat reduction through deforestation by the Polynesians as well as the European colonizers. ^[6]

Distribution

(Petroica australis) is endemic to New Zealand, as in both native to and confined to this region. Historically, (P. australis) inhabited much of lowland New Zealand. Due to habitat loss and introduced predation, their distribution has become much more patchy. ^[6] The South Island robin has fared slightly better than the Stewart Island robin. There are two populations on the east coast of the island ^[7], and slightly more common in the north and west. ^[1]) However, the Stewart Island robin has been relegated to 3 subpopulations all in the Leptospermum swamp scrubland. Although this habitat is not their preferred, it is less heavily populated by mammalian predators. At one point got down to less than 500 individuals on the whole island. ^[8] Some of these birds have since been translocated to other islands which lack introduced predators (rats, stoats, bushtail possums) such as Ulva Island, Motuara Island, and Nukuwaiata Island, where they have been relatively successful at establishing new populations (around 600 individuals on Motuara alone). ^[9] On the South Island, (P. australis) has a strong affinity for Douglas fir plantations, in comparison with native forests (kanuka trees) or Monterey pine plantations. Above all else, this appears to be due to forest structure rather than strict food availability or viable nesting sites. They prefer structurally simple forests with dense, even canopies, and ground covered with leaf litter. ^[6] When the population was introduced to Ulva Island, there tended to be increased nesting with increasing presence of broad-leaved coastal vegetation, though their primary reasons for settling in a certain place still seemed to be structure of vegetation, as robins have a high degree of nesting flexibility. ^[7]

Ecology, Life History, Behavior

Invertebrates, including earthworms, beetles, and other arthropods comprise most of the robins’ diet. ^[5] They forage for these among the leaf litter covering their habitat’s ground. They have also been observed to eat berries from time to time; however, they do not cache berries. They do cache their invertebrate prey whole or in portions. They do this singly at different sites and do not cache more than once at a particular site. They typically store their prey with 10 meters of where they killed it, even if they are not within their own territory. In the winter their primary cache is earthworms, and during the summer it trends more toward cicadas. They have a very good memory of their storage sites; a male has been observed to find as many as five caches successively before returning the stores to his mate during incubation. ^[10] New Zealand robins have demonstrated an ability to differentiate and prioritize caches of varying sizes, up to 12 total items, without any training. In fact, these robins have the highest numerical competency of any recorded wild animal, which they can use to return to the biggest caches first, followed by less rewarding ones. ^[11] After storage, a robin will typically return to hunting, unless a particularly large prey was captured and stored, in which case it might preen or rest for a while. Usually robins will not return to a certain cache if it has been more than four days since the kill; the rare exception is an earthworm, which the robin might retrieve after several days. Because of its high metabolic rate, a robin might spend as much as 90% of its day foraging or storing during the winter. ^[10]

New Zealand 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 on one territory will compete for food resources during non-breeding times. Since they use slightly different methods for foraging, some competition is reduced. However, they can and will steal from their mate’s cache if given the opportunity.^[10] Males do dominate females, and thus will aggressively exclude females from food, such that females will only access food sources when unattended by the males. ^[12] During breeding season, as the female is solely responsible for nest building and incubation, the male will bring the female and the hatchlings food. ^[2] Therefore, males will cache less than females at this time but more than females during non-breeding (females’ cache amounts remain mostly stable year-round). ^[12]

For reproduction, robins have some fairly interesting characteristics which help them, to some extent, recover from predation. Robins become sexually mature between six and 12 months. They begin their breeding season fairly early in August or September, which is aided by their food stores (otherwise they would have to spend too much time hunting for food this early in in the spring).^[10] They build open-cup nests in tree-forks or inside tree cavities.^[7] Incubation lasts 18 days, and chicks leave the nest after 21 days. Five to 25 days after fledglings leave the nest, the pair may breed again. A modal clutch size is two eggs ^[13] with the expected tradeoffs between size and number of eggs observed (greater the size, the fewer the eggs). ^[14] Because females remain with the nest and hatchlings for so long, both she and her young are susceptible to predation. If the female survives, however, she and her mate can reproduce more quickly (3-10 days) than after a normal clutch leaves the nest, making it a little bit easier to recover from the predation. ^[2]

A male’s call during non-breeding season is a downscale, which means that it is a series of loud notes with descending frequency which start in rapid succession and finish slowly. During breeding season, the males resort to full song to court the females. Full song is a loud, clear, and continuous song which can last for more than 30 minutes with very brief pauses. Full song is typically sung from the canopy or an emergent tree. ^[2] Singing is also seemingly performed as part of a strategic regulation of body mass. While robins sing during the morning chorus as well as throughout the day, they seem to increase their singing according to food availability. When they have had more food, they will increase energetic behaviors such as singing in order to arrive at a strategic mass by dusk. Thus, even though two robins might begin the day with different weights, they will end the day with similar weights. A side effect of this behavior 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. ^[4]

Other than foraging for invertebrates on the forest floor, a New Zealand robin might also spend its time vegetation gleaning (4.5%), hawking (0.3%) or fly-catching (0.1%) in order to find food. ^[6] Outside of collecting food resources, a robin also engages in a few body maintenance activities during the day. It spends about 0.5% of its time bathing, 0.04% anting (using ants or millipedes, which it sometimes eats afterwards), and some adults sun bathe, though this behavior does not seem to be essential as juveniles do not engage in it at all. ^[15] A New Zealand robin is also relatively long-lived, as it can survive up to 14 years where few or no predators exist. ^[13]

Conservation

While the New Zealand robin ((Petroica australis)) is apparently not on the IUCN’s list for threatened species, 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. ^[7] Because of this sharp decline in population, on Stewart Island, several attempts have been made to translocate the Stewart Island robin to other islands nearby where introduced predators do not exist or have been eradicated. Some of these islands include Ulva, Motuara, and Nukuwaiata islands. However, many of these translocations have involved 12 or fewer colonizing individuals, such that inbreeding is nearly unavoidable. This has led to some apparent immunocompetency issues, as well as reproduction problems. On Motuara Island, there have been high hatch failures, as well as fewer clutches. Also, even though the parasite loads between these bottlenecked populations and their source populations, the immune response on a cellular level is not as strong for the bottlenecked population.^[9] Therefore, there is a huge concern that, although some of these populations are indeed growing, that there might be too much inbreeding so things like immune and reproduction systems and thoroughly compromised. On the other hand, the South Island robin, although its distribution on the island is increasingly fragmented, does not show much genetic loss in comparison with historical populations. ^[16] Thus, it might be a slightly better situation than its Stewart Island sister.

Gallery

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  Stewart Island Robin

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  South Island Robin

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  Stewart Island Robin

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  South Island Robin

References

1. ^ ^{a b c d} Miller, Hilary C. & Lambert, David M. (2006): A molecular phylogeny of New Zealand’s Petroica (Aves: Petroicidae) species based on mitochondrial DNA sequences. Molecular Phylogenetics and Evolution 40(3): 844-855. doi:10.1016/j.ympev.2006.04.012 (HTML abstract)
2. ^ ^{a b c d} Powlesland, R. G. (1997): Protocols for monitoring New Zealand robins: Petroica australis. Department of Conservation of Technical Series 13
3. ^ BirdLife International (2004). Petroica australis. 2006. IUCN Red List of Threatened Species. IUCN 2006. www.iucnredlist.org. Retrieved on 12 May 2006. Database entry includes a range map and justification for why this species is of least concern
4. ^ ^{a b} Barnett, Craig A. & Briskie, James V. (2011): Strategic Regulation of Body Mass and Singing Behavior in New Zealand Robins. Ethology 117 (1): 28.
5. ^ ^{a b} Worthy, Trevor H & Holdaway, Richard N. (2002): Shorebirds, Parrots and Passerines. The Lost World of the Moa: 410-440.
6. ^ ^{a b c d} Borkin, Kerry M. et al (2008): South Island robin (Petroica australis australis) abundance and leaf-litter invertebrates in plantation and native forest. Notornis 54 (2): 65.
7. ^ ^{a b c d} Steffens, K. E. et al. (2005): Habitat selection by South Island saddlebacks and Stewart Island robins reintroduced to Ulva Island, New Zealand. Journal of Ecology 29: 221–229.
8. ^ Laws, R. J. & Jamieson, I. G. (2011): Is lack of evidence of inbreeding depression in a threatened New Zealand robin indicative of reduced genetic load? Animal Conservation 14 (1): 47.
9. ^ ^{a b} Hale, K. A & Briskie, J. V. (2007): Decreased immunocompetence in a severely bottlenecked population of an endemic New Zealand bird. Animal Conservation 10 (1): 2-10.
10. ^ ^{a b c d} Powlesland, R. G. (1980): Food-Storing Behavior of the South Island Robin. Mauri Ora 8 : 11.
11. ^ Hunt, Simon & Low, Jason & Burns, K.C. (2008): Adaptive numerical competency in a food-hoarding songbird. Royal Society of London. Proceedings. Biological Sciences 275 (1649): 2373-2379.
12. ^ ^{a b} Steer, Jamie & Burns, KC. (2008): Seasonal variation in male-female competition, cooperation and selfish hoarding in a monogamous songbird. Behavioral Ecology & Sociobiology 62 (7): 1175.
13. ^ ^{a b} Taylor, S. S. et al (2007): Historic and contemporary levels of genetic variation in two New Zealand passerines with different histories of decline. Journal of Evolutionary Biology 20 (5): 2035.
14. ^ Boulton, Rebecca L.& Powlesland, Ralph G. (2008): Variation in egg size and nest survival with female age in the South Island Robin Petroica australis. Ibis 150 (4): 824.
15. ^ Powlesland, R. G. (1983): Body maintenance activities of the South Island robin. Emu 82 : 296.
16. ^ Taylor, Sabrina S et al (2008): Genetic monogamy in two long-lived New Zealand passerines. Journal of Avian Biology 39 (5): 579-583.

External links

• Toutouwai