The Mariana crow (''Corvus kubaryi'') ( Chamorro name: ''åga'') is a

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

of the

crow family Corvidae is a Cosmopolitan distribution, cosmopolitan Family (biology), family of Songbird, oscine passerine birds that contains the crows, ravens, Rook (bird), rooks, magpies, jackdaws, jays, treepies, choughs, and Nutcracker (bird), nutcrackers ...

from the tropical Western

Pacific The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean, or, depending on the definition, to Antarctica in the south, and is bounded by the cont ...

. It is a glossy black bird about long and known only from the islands of

Guam Guam ( ; ) is an island that is an Territories of the United States, organized, unincorporated territory of the United States in the Micronesia subregion of the western Pacific Ocean. Guam's capital is Hagåtña, Guam, Hagåtña, and the most ...

and Rota. It is a rare bird which has steadily declined in numbers since the 1960s. On Guam there are no remaining native Mariana Crows, the population having been decimated by the introduction of the

brown tree snake The brown tree snake (''Boiga irregularis''), also known as the brown catsnake, is an arboreal rear-fanged colubrid snake native to eastern and northern coastal Australia, eastern Indonesia (Sulawesi to Papua), Papua New Guinea, and many island ...

. On Rota the population has declined to fewer than 200 individuals, the main threats here being the reduction of suitable habitat because of development and predation. Despite translocations from Rota to the

Guam National Wildlife Refuge The Guam National Wildlife Refuge is composed of three units: the Andersen Air Force Base Overlay Unit (Air Force Overlay Unit), the Navy Overlay Unit, and the Ritidian Unit. The Ritidian Unit ( CHamoru: ''Puntan Litekyan'') is on the northernmo ...

in the late 1990s and early 2000s, by 2011 the Mariana Crow was extirpated from Guam. Current conservation efforts on Rota include habitat protection, and a captive rear-and-release program. The

International Union for Conservation of Nature The International Union for Conservation of Nature (IUCN) is an international organization working in the field of nature conservation and sustainable use of natural resources. Founded in 1948, IUCN has become the global authority on the stat ...

has rated the bird as being "

critically endangered An IUCN Red List critically endangered (CR or sometimes CE) species is one that has been categorized by the International Union for Conservation of Nature as facing an extremely high risk of extinction in the wild. As of December 2023, of t ...

Description

The Mariana crow is a small black

crow A crow is a bird of the genus ''Corvus'', or more broadly, a synonym for all of ''Corvus''. The word "crow" is used as part of the common name of many species. The related term "raven" is not linked scientifically to any certain trait but is rathe ...

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 and is about long. The Mariana crow has a variety of vocalizations, including two locational calls used to maintain contact between pairs, family members and

flock Flock, flocks or flocking may refer to: * Flock (birds), a gathering of individual birds to forage or travel collectively Arts and entertainment Music * ''Flock'' (Bell X1 album), 2005 * ''Flock'' (Jane Weaver album), 2021 * The Flock (band), ...

mates. These locational calls are either a high-pitched series of one to three ''caw'' or ''hi'' sounds, or a series of longer ''caw'' sounds with a nasal ''aaa'' element to the call; the latter call may be used exclusively between mated pairs. Alarm calls are a rapid series of sharp ''caw''s. The birds also make a variety of squalling, guttural sounds, which may be done either quietly or excitedly.

Distribution and ecology

The Mariana crow inhabits second growth and mature forests, as well as coastal strand vegetation, but nests only in native limestone forest. It preferentially nests in the crowns of two canopy- emergent tree species: yoga tree ('' Elaeocarpus joga'') and the

fig The fig is the edible fruit of ''Ficus carica'', a species of tree or shrub in the flowering plant family Moraceae, native to the Mediterranean region, together with western and southern Asia. It has been cultivated since ancient times and i ...

Ficus prolixa ''Ficus'' ( or ) is a genus of about 850 species of woody trees, shrubs, vines, epiphytes and hemiepiphytes in the family Moraceae. Collectively known as fig trees or figs, they are native throughout the tropics with a few species extending int ...

''. The crow currently is only found on the island of Rota. It disappeared from southern Guam in the 1960s and from central Guam in the 1970s, mostly inhabiting

Andersen Air Force Base Andersen Air Force Base (Andersen AFB, AAFB) is a United States Air Force base located primarily within the village of Yigo in the United States territory of Guam. The host unit at Andersen AFB is the 36th Wing (36 WG), assigned to the Pacif ...

. Its population on Rota has also decreased.

Diet

Extremely versatile, the Mariana crow is an opportunistic

omnivore An omnivore () is an animal that regularly consumes significant quantities of both plant and animal matter. Obtaining energy and nutrients from plant and animal matter, omnivores digest carbohydrates, protein, fat, and fiber, and metabolize t ...

, feeding on

insect Insects (from Latin ') are Hexapoda, hexapod invertebrates of the class (biology), class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body (Insect morphology#Head, head, ...

lizard Lizard is the common name used for all Squamata, squamate reptiles other than snakes (and to a lesser extent amphisbaenians), encompassing over 7,000 species, ranging across all continents except Antarctica, as well as most Island#Oceanic isla ...

s, other birds'

egg An egg is an organic vessel grown by an animal to carry a possibly fertilized egg cell (a zygote) and to incubate from it an embryo within the egg until the embryo has become an animal fetus that can survive on its own, at which point the ...

hermit crab Hermit crabs are anomuran Decapoda, decapod crustaceans of the superfamily (taxonomy), superfamily Paguroidea that have adapted to occupy empty scavenged mollusc shells to protect their fragile exoskeletons. There are over 800 species of hermit c ...

fruit In botany, a fruit is the seed-bearing structure in flowering plants (angiosperms) that is formed from the ovary after flowering. Fruits are the means by which angiosperms disseminate their seeds. Edible fruits in particular have long propaga ...

s, and

seed In botany, a seed is a plant structure containing an embryo and stored nutrients in a protective coat called a ''testa''. More generally, the term "seed" means anything that can be Sowing, sown, which may include seed and husk or tuber. Seeds ...

Nesting

The Mariana crow begins nesting as early as July and as late as May. The nest is a large, cupped platform of small sticks, lined with leaf fibers. Clutch size varies from 1 to 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

(''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

rat Rats are various medium-sized, long-tailed rodents. Species of rats are found throughout the order Rodentia, but stereotypical rats are found in the genus ''Rattus''. Other rat genera include '' Neotoma'' (pack rats), '' Bandicota'' (bandicoo ...

s, the

Mariana monitor ''Varanus tsukamotoi'', the Mariana monitor or Saipan monitor, is a species of lizard of the family (biology), family Varanidae. It is Endemism, endemic to the Northern Mariana Islands and Guam, and has been introduced to Japan in the Marshall Is ...

lizard (''Varanus tsukamotoi''),

typhoon A typhoon is a tropical cyclone that develops between 180° and 100°E in the Northern Hemisphere and which produces sustained hurricane-force winds of at least . This region is referred to as the Northwestern Pacific Basin, accounting for a ...

s, predation from

feral cat A feral cat or a stray cat is an unowned domestic cat (''Felis catus'') that lives outdoors and avoids human contact; it does not allow itself to be handled or touched, and usually remains hidden from humans. Feral cats may breed over dozens ...

s, disease, and competition with the black drongo (''Dicrurus macrocercus''). More recently, the brown tree snake has also been detected on 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 The National Wildlife Refuge System (NWRS) is a system of protected areas of the United States managed by the United States Fish and Wildlife Service (FWS), an agency within the United States Department of the Interior, Department of the Interi ...

was established on Guam to preserve the remaining forest, and birds were translocated from Rota. Biologically controlling the brown tree snake is also being discussed. Crows were transported from Rota to Guam in 2003 to assist conservation efforts though this may have had the unintended side effect of decreasing genetic variation within the species as tests have shown the Rota population is less diverse than the Guam. Formerly classified as an

endangered An endangered species is a species that is very likely to become extinct in the near future, either worldwide or in a particular political jurisdiction. Endangered species may be at risk due to factors such as habitat loss, poaching, inv ...

species by the

IUCN The International Union for Conservation of Nature (IUCN) is an international organization working in the field of nature conservation and sustainable use of natural resources. Founded in 1948, IUCN has become the global authority on the status ...

, 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

status in 2008 as it is in immediate danger of

extinct Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...

ion, numbering so few birds that it could be entirely wiped out by a single catastrophic event such as an epidemic of

West Nile virus West Nile virus (WNV) is a single-stranded RNA virus that causes West Nile fever. It is a member of the family ''Flaviviridae'', from the genus ''Flavivirus'', which also contains the Zika virus, dengue virus, and yellow fever virus. The virus ...

References

{{Authority control

Mariana crow The Mariana crow (''Corvus kubaryi'') ( Chamorro name: ''åga'') is a species of the crow family from the tropical Western Pacific. It is a glossy black bird about long and known only from the islands of Guam and Rota. It is a rare bird which ...

Birds of Micronesia Critically endangered fauna of Oceania