Mariana Crow
Encyclopedia
The Mariana Crow is a species
of the crow family
from the north Pacific
. It is an endangered species
which has steadily declined in numbers since the 1960s.
with a bluish-black gloss on its tail, and a greenish-black gloss on its back, underparts, head, and wings. In general, females are smaller than males. An adult weighs about 9 ounces (250 grams) and is about 15 inches (38 centimetres) long.
The voice is a loud scream of kaaa-ah.
, and Rota
in the Northern Marianas Islands where it preferentially nests in the crowns of two canopy-emergent tree species: Yoga Tree (Elaeocarpus joga) and the fig
Ficus prolixa.
, feeding on insects, lizards, other birds' eggs, hermit crabs, fruits, and seeds.
(Boiga irregularis). In spite of protection of nesting-sites by electrical tree barriers, the remaining birds are considered to be reproductively senescent. On Rota, many other threats endanger the crow, including homestead development, resort and golf-course construction, agricultural settlement, nest-predation from introduced rats, the Mangrove Monitor lizard (Varanus indicus), typhoons, disease, and competition with the Black Drongo
(Dicrurus macrocercus). More recently, the Brown Tree Snake has also been introduced to Rota, likely leading to serious declines in the Mariana Crow population there if the snake population establishes itself. The Mariana Crow is also persecuted by residents of both islands who see it as an obstacle to development.
In 1993, a National Wildlife Refuge
was established on Guam to preserve the remaining forest, and birds are being translocated from Rota. Biologically controlling the Brown Tree Snake is also being discussed.
Formerly classified as an Endangered species by the IUCN, it was suspected to be rarer than generally assumed. Following the evaluation of its status, this was found to be correct, and it is consequently uplisted to Critically Endangered
status in 2008 as it is in immediate danger of extinction, numbering so few birds that it might be entirely wiped out by a single catastrophic event such as an epidemic of West Nile Virus
.
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
of the crow family
Corvidae
Corvidae is a cosmopolitan family of oscine passerine birds that contains the crows, ravens, rooks, jackdaws, jays, magpies, treepies, choughs and nutcrackers. The common English names used are corvids or the crow family , and there are over 120 species...
from the north Pacific
Pacific Ocean
The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...
. It is an endangered species
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...
which has steadily declined in numbers since the 1960s.
Description
The Mariana Crow is a small black crowCrow
Crows form the genus Corvus in the family Corvidae. Ranging in size from the relatively small pigeon-size jackdaws to the Common Raven of the Holarctic region and Thick-billed Raven of the highlands of Ethiopia, the 40 or so members of this genus occur on all temperate continents and several...
with a bluish-black gloss on its tail, and a greenish-black gloss on its back, underparts, head, and wings. In general, females are smaller than males. An adult weighs about 9 ounces (250 grams) and is about 15 inches (38 centimetres) long.
The voice is a loud scream of kaaa-ah.
Distribution and ecology
The Mariana Crow inhabits second growth and mature forests, as well as coastal strand vegetations, but nests only in native limestone forest. It lives primarily in the northern end of the island of GuamGuam
Guam is an organized, unincorporated territory of the United States located in the western Pacific Ocean. It is one of five U.S. territories with an established civilian government. Guam is listed as one of 16 Non-Self-Governing Territories by the Special Committee on Decolonization of the United...
, and Rota
Rota (island)
Rota also known as the "peaceful island", is the southernmost island of the United States Commonwealth of the Northern Mariana Islands and the second southernmost of the Marianas Archipelago. It lies approximately 40 miles north-northeast of the United States territory of Guam...
in the Northern Marianas Islands where it preferentially nests in the crowns of two canopy-emergent tree species: Yoga Tree (Elaeocarpus joga) and the fig
Ficus
Ficus is a genus of about 850 species of woody trees, shrubs, vines, epiphytes, and hemiepiphyte in the family Moraceae. Collectively known as fig trees or figs, they are native throughout the tropics with a few species extending into the semi-warm temperate zone. The Common Fig Ficus is a genus of...
Ficus prolixa.
Diet
Extremely versatile, the Mariana Crow is an opportunistic omnivoreOmnivore
Omnivores are species that eat both plants and animals as their primary food source...
, feeding on insects, lizards, other birds' eggs, hermit crabs, fruits, and seeds.
Nesting
The Mariana Crow begins nesting as early as July and as late as March. The nest is a large, cupped platform of small sticks, lined with leaf fibers. Clutch size varies from 1-4 eggs, and both parents incubate the eggs, brood the chicks, and care for the juveniles even after they fledge. Parental care has been known to range from 5 to 18 months, and juveniles may take as long as 3 years before entering the adult breeding cycle.Status and conservation
On Guam, the Mariana Crow's decline is primarily due to predation by the introduced Brown Tree SnakeBrown tree snake
The brown tree snake is an arboreal rear-fanged colubrid snake native to eastern and northern coastal Australia, Papua New Guinea, and a large number of islands in northwestern Melanesia....
(Boiga irregularis). In spite of protection of nesting-sites by electrical tree barriers, the remaining birds are considered to be reproductively senescent. On Rota, many other threats endanger the crow, including homestead development, resort and golf-course construction, agricultural settlement, nest-predation from introduced rats, the Mangrove Monitor lizard (Varanus indicus), typhoons, disease, and competition with the Black Drongo
Black Drongo
The Black Drongo , also known as the King Crow, is a small Asian passerine bird of the drongo family Dicruridae. Previously considered a subspecies of the African Fork-tailed Drongo , it is now recognized as a full species...
(Dicrurus macrocercus). More recently, the Brown Tree Snake has also been introduced to Rota, likely leading to serious declines in the Mariana Crow population there if the snake population establishes itself. The Mariana Crow is also persecuted by residents of both islands who see it as an obstacle to development.
In 1993, a National Wildlife Refuge
National Wildlife Refuge
National Wildlife Refuge is a designation for certain protected areas of the United States managed by the United States Fish and Wildlife Service. The National Wildlife Refuge System is the world's premiere system of public lands and waters set aside to conserve America's fish, wildlife and plants...
was established on Guam to preserve the remaining forest, and birds are being translocated from Rota. Biologically controlling the Brown Tree Snake is also being discussed.
Formerly classified as an Endangered species by the IUCN, it was suspected to be rarer than generally assumed. Following the evaluation of its status, this was found to be correct, and it is consequently uplisted to Critically Endangered
Critically Endangered
Critically Endangered is the highest risk category assigned by the IUCN Red List for wild species. Critically Endangered means that a species' numbers have decreased, or will decrease, by 80% within three generations....
status in 2008 as it is in immediate danger of extinction, numbering so few birds that it might be entirely wiped out by a single catastrophic event such as an epidemic of West Nile Virus
West Nile virus
West Nile virus is a virus of the family Flaviviridae. Part of the Japanese encephalitis antigenic complex of viruses, it is found in both tropical and temperate regions. It mainly infects birds, but is known to infect humans, horses, dogs, cats, bats, chipmunks, skunks, squirrels, domestic...
.