Black Robin
Encyclopedia
The Black Robin or Chatham Island Robin (Petroica traversi) is an endangered bird
from the Chatham Islands
off the east coast of New Zealand
. It is closely related to the New Zealand Robin
(P. australis). It was first described by Walter Buller
in 1872. The binomial commemorates the New Zealand botanist Henry H. Travers
(1844–1928). The Black Robin is a sparrow
-sized bird measuring 14–15 cm (5.5–6 in). Its plumage is almost entirely brownish-black, with a black bill and brownish-black yellow-soled feet. Unlike its mainland counterparts, its flight capacity is somewhat reduced. Evolution in the absence of mammalian predators made it vulnerable to introduced species such as cats and rats, and it became extinct on the main island of the Chatham group before 1871, being restricted to Little Mangere Island
thereafter.
and his Wildlife Service
team, and by "Old Blue", the last remaining fertile female. The remaining birds were moved to Mangere Island
. They increased the annual output of Old Blue (and later other females) by removing the first clutch
over every year and placing the eggs in the nest of the Chatham race of the Tomtit
, a technique known as cross-fostering
. The Tomtits raised the first brood, and the Black Robins, having lost their eggs, relaid and raised another brood.
All of the surviving black robins are descended from "Old Blue", unfortunately giving little genetic variation among the population and creating an extreme population bottleneck
. Interestingly, this seems to have caused no inbreeding
problems, leading to speculation that the species has passed through several such population reductions in its evolutionary past and thus losing any alleles that could cause deleterious inbreeding effects. It was generally assumed that the minimum viable population
protecting from inbreeding depression
was around 50 individuals, but this is now known to be an inexact average, with the actual numbers being below 10 in rapidly-reproducing small-island species such as the Black Robin, to several hundred in long-lived continental species with a wide distribution (such as elephant
s or tiger
s).
The species is still endangered
, but now numbers around 250 individuals in populations on Mangere Island and South East Island
. Ongoing restoration of habitat and eradication of introduced predators is being undertaken so that the population of this and other endangered Chatham endemic
s can be spread to several populations, decreasing the risk of extinction by natural disasters or similar stochastic
events.
The female Black Robin usually lays two eggs
Bird
Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...
from the Chatham Islands
Chatham Islands
The Chatham Islands are an archipelago and New Zealand territory in the Pacific Ocean consisting of about ten islands within a radius, the largest of which are Chatham Island and Pitt Island. Their name in the indigenous language, Moriori, means Misty Sun...
off the east coast of New Zealand
New Zealand
New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...
. It is closely related to the New Zealand Robin
New Zealand Robin
The New Zealand Robin or Toutouwai , 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...
(P. australis). It was first described by Walter Buller
Walter Buller
Walter Lawry Buller KCMG was a New Zealand lawyer, naturalist and ornithologist.Buller was the author of A History of the Birds of New Zealand , with illustrations by John Gerrard Keulemans. In 1882 he produced the Manual of the Birds of New Zealand as a cheaper, popular alternative...
in 1872. The binomial commemorates the New Zealand botanist Henry H. Travers
Henry H. Travers
Henry Hammersley Travers was a New Zealand naturalist, professional collector and taxidermist. He was the son of the politician William Travers.Specimens collected by Travers are in the collection of the Museum of New Zealand Te Papa Tongarewa...
(1844–1928). The Black Robin is a sparrow
House Sparrow
The House Sparrow is a bird of the sparrow family Passeridae, found in most parts of the world. One of about 25 species in the genus Passer, the House Sparrow occurs naturally in most of Europe, the Mediterranean region, and much of Asia...
-sized bird measuring 14–15 cm (5.5–6 in). Its plumage is almost entirely brownish-black, with a black bill and brownish-black yellow-soled feet. Unlike its mainland counterparts, its flight capacity is somewhat reduced. Evolution in the absence of mammalian predators made it vulnerable to introduced species such as cats and rats, and it became extinct on the main island of the Chatham group before 1871, being restricted to Little Mangere Island
Little Mangere Island
Little Mangere Island or Tapuaenuku is part of the Chatham Islands chain, located east of New Zealand's South Island. The island lies off the west coast of Pitt Island, south-east of the chain's main settlement, Waitangi, on Chatham Island...
thereafter.
Conservation
There are now around 250 black robins but in 1980 only five survived on Little Mangere Island. They were saved from extinction by Don MertonDon Merton
Donald Merton, QSM was a New Zealand conservationist best known for saving the black robin from extinction. He also discovered the lek breeding system of the kakapo....
and his Wildlife Service
New Zealand Wildlife Service
The New Zealand Wildlife Service is a defunct government department that was replaced by the Department of Conservation in 1987.-External links:* - New Zealand Wildlife Service collection...
team, and by "Old Blue", the last remaining fertile female. The remaining birds were moved to Mangere Island
Mangere Island
Mangere Island is part of the Chatham Islands archipelago, located east of New Zealand's South Island and has an area of . The island lies off the west coast of Pitt Island, south-east of the main settlement in the Chathams, Waitangi, on Chatham Island....
. They increased the annual output of Old Blue (and later other females) by removing the first clutch
Clutch (eggs)
A clutch of eggs refers to all the eggs produced by birds or reptiles, often at a single time, particularly those laid in a nest.In birds, destruction of a clutch by predators, , results in double-clutching...
over every year and placing the eggs in the nest of the Chatham race of the Tomtit
Tomtit
The Tomtit, Petroica macrocephala, is a small passerine bird in the family Petroicidae, the Australian robins. It is endemic to the islands of New Zealand, ranging across the main islands as well as several of the outlying islands. It has several other English names as well. There are several...
, a technique known as cross-fostering
Cross-fostering
Cross-fostering is a technique used in animal husbandry, animal science, genetic and nature versus nurture studies, and conservation, whereby offspring are removed from their biological parents at birth and raised by surrogates. This can also occasionally occur in nature.-Animal...
. The Tomtits raised the first brood, and the Black Robins, having lost their eggs, relaid and raised another brood.
All of the surviving black robins are descended from "Old Blue", unfortunately giving little genetic variation among the population and creating an extreme population bottleneck
Population bottleneck
A population bottleneck is an evolutionary event in which a significant percentage of a population or species is killed or otherwise prevented from reproducing....
. Interestingly, this seems to have caused no inbreeding
Inbreeding
Inbreeding is the reproduction from the mating of two genetically related parents. Inbreeding results in increased homozygosity, which can increase the chances of offspring being affected by recessive or deleterious traits. This generally leads to a decreased fitness of a population, which is...
problems, leading to speculation that the species has passed through several such population reductions in its evolutionary past and thus losing any alleles that could cause deleterious inbreeding effects. It was generally assumed that the minimum viable population
Minimum Viable Population
Minimum viable population is a lower bound on the population of a species, such that it can survive in the wild. This term is used in the fields of biology, ecology, and conservation biology...
protecting from inbreeding depression
Inbreeding depression
Inbreeding depression is the reduced fitness in a given population as a result of breeding of related individuals. It is often the result of a population bottleneck...
was around 50 individuals, but this is now known to be an inexact average, with the actual numbers being below 10 in rapidly-reproducing small-island species such as the Black Robin, to several hundred in long-lived continental species with a wide distribution (such as elephant
Elephant
Elephants are large land mammals in two extant genera of the family Elephantidae: Elephas and Loxodonta, with the third genus Mammuthus extinct...
s or tiger
Tiger
The tiger is the largest cat species, reaching a total body length of up to and weighing up to . Their most recognizable feature is a pattern of dark vertical stripes on reddish-orange fur with lighter underparts...
s).
The species is still endangered
Endangered species
An endangered species is a population of organisms which is at risk of becoming extinct because it is either few in numbers, or threatened by changing environmental or predation parameters...
, but now numbers around 250 individuals in populations on Mangere Island and South East Island
South East Island/Rangatira
South East Island/Rangatira is the third largest island in the Chatham Islands chain, and covers an area of . It is located east of New Zealand's South Island...
. Ongoing restoration of habitat and eradication of introduced predators is being undertaken so that the population of this and other endangered Chatham endemic
Endemic (ecology)
Endemism is the ecological state of being unique to a defined geographic location, such as an island, nation or other defined zone, or habitat type; organisms that are indigenous to a place are not endemic to it if they are also found elsewhere. For example, all species of lemur are endemic to the...
s can be spread to several populations, decreasing the risk of extinction by natural disasters or similar stochastic
Stochastic
Stochastic refers to systems whose behaviour is intrinsically non-deterministic. A stochastic process is one whose behavior is non-deterministic, in that a system's subsequent state is determined both by the process's predictable actions and by a random element. However, according to M. Kac and E...
events.
The female Black Robin usually lays two eggs