''Varanus tsukamotoi'', the Mariana monitor or Saipan monitor, is a

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

lizard Lizards are a widespread group of squamate reptiles, with over 7,000 species, ranging across all continents except Antarctica, as well as most oceanic island chains. The group is paraphyletic since it excludes the snakes and Amphisbaenia alt ...

of the

Varanidae The Varanidae are a family of lizards in the superfamily Varanoidea within the Anguimorpha group. The family, a group of carnivorous and frugivorous lizards, includes the living genus '' Varanus'' and a number of extinct genera more closely relat ...

family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...

. It is

endemic Endemism is the state of a species being found in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also found elsew ...

to the

Northern Mariana Islands The Northern Mariana Islands, officially the Commonwealth of the Northern Mariana Islands (CNMI; ch, Sankattan Siha Na Islas Mariånas; cal, Commonwealth Téél Falúw kka Efáng llól Marianas), is an unincorporated territory and commonw ...

and

Guam Guam (; ch, Guåhan ) is an organized, unincorporated territory of the United States in the Micronesia subregion of the western Pacific Ocean. It is the westernmost point and territory of the United States (reckoned from the geographic cent ...

, and has been introduced to Japtan in the

Marshall Islands The Marshall Islands ( mh, Ṃajeḷ), officially the Republic of the Marshall Islands ( mh, Aolepān Aorōkin Ṃajeḷ),'' () is an independent island country and microstate near the Equator in the Pacific Ocean, slightly west of the Internati ...

Etymology

It was named by

Kyukichi Kishida was a Japanese zoologist, who published in mammalogy and arachnology. He described several spider genera or species including : * ''Heptathela ''Heptathela'' is a genus of spiders that includes the Kimura spider (''Heptathela kimurai''). Th ...

after Dr. Iwasaburo Tsukamoto, who supported his expedition to the South Pacific. In the

Chamorro Chamorro may refer to: * Chamorro people, the indigenous people of the Mariana Islands in the Western Pacific * Chamorro language, an Austronesian language indigenous to The Marianas * Chamorro Time Zone, the time zone of Guam and the Northern Mar ...

language, it is known as ''hilitai''.

Taxonomy

Along with the closely related '' Varanus bennetti'', it was long considered a population of the mangrove monitor (''V. indicus'') that had been introduced from the East Indies to smaller Pacific islands by

Polynesians Polynesians form an ethnolinguistic group of closely related people who are native to Polynesia (islands in the Polynesian Triangle), an expansive region of Oceania in the Pacific Ocean. They trace their early prehistoric origins to Island Sou ...

to provide a meat supply. However, other scientists maintained that this would not be likely, as the monitors would compete with humans for food, grow slowly, and yield little meat. The presence of a native

name for the species (''hilitai'') also indicates that it would have either been present on the islands when they arrived, or the Chamorro would have brought the species with them. Phylogenetic analysis has also affirmed monitors being native to Micronesia, having colonized the islands and diverged from the ''Varanus indicus''

species complex In biology, a species complex is a group of closely related organisms that are so similar in appearance and other features that the boundaries between them are often unclear. The taxa in the complex may be able to hybridize readily with each oth ...

during the

Late Pleistocene The Late Pleistocene is an unofficial Age (geology), age in the international geologic timescale in chronostratigraphy, also known as Upper Pleistocene from a Stratigraphy, stratigraphic perspective. It is intended to be the fourth division of ...

Distribution

It is native to

Cocos Island Cocos Island ( es, Isla del Coco) is an island in the Pacific Ocean administered by Costa Rica, approximately southwest of the Costa Rican mainland. It constitutes the 11th of the 13 districts of Puntarenas Canton of the Province of Puntarenas ...

Saipan Saipan ( ch, Sa’ipan, cal, Seipél, formerly in es, Saipán, and in ja, 彩帆島, Saipan-tō) is the largest island of the Northern Mariana Islands, a Commonwealth (U.S. insular area), commonwealth of the United States in the western Pa ...

, Rota,

Pagan Paganism (from classical Latin ''pāgānus'' "rural", "rustic", later "civilian") is a term first used in the fourth century by early Christians for people in the Roman Empire who practiced polytheism, or ethnic religions other than Judaism. ...

Tinian Tinian ( or ; old Japanese name: 天仁安島, ''Tenian-shima'') is one of the three principal islands of the Commonwealth of the Northern Mariana Islands. Together with uninhabited neighboring Aguiguan, it forms Tinian Municipality, one of th ...

, and

Anatahan Anatahan is an island in the Northern Mariana Islands in the Pacific Ocean, and has one of the most active volcanoes of the archipelago. Although formerly inhabited, the island is currently uninhabited due to the constant danger of volcanic er ...

in the

Mariana Islands The Mariana Islands (; also the Marianas; in Chamorro: ''Manislan Mariånas'') are a crescent-shaped archipelago comprising the summits of fifteen longitudinally oriented, mostly dormant volcanic mountains in the northwestern Pacific Ocean, betw ...

, and is also known from Japtan Island in the

, where it likely originates from a human introduction. An alleged record from the

Bonin Islands The Bonin Islands, also known as the , are an archipelago of over 30 subtropical and tropical islands, some directly south of Tokyo, Japan and northwest of Guam. The name "Bonin Islands" comes from the Japanese word ''bunin'' (an archaic readi ...

Japan Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the north ...

is thought to be erroneous. For unknown reasons, this species is not present on

Sarigan Sarigan is an uninhabited volcanic island in the Pacific Ocean. It is part of the Northern Mariana Islands, a U.S. territory. Sarigan is located northeast of Anatahan island, south of Guguan and north of Saipan, the largest island in the Nor ...

Island despite being present on adjacent islands; the monitor species on that island is instead thought to be

Bennett's long-tailed monitor Bennett's long-tailed monitor (''Varanus bennetti'') is a species of monitor lizard in the family Varanidae. It is found in Palau, the Federated States of Micronesia, and the Northern Mariana Islands. Etymology The specific epithet, ''bennet ...

(''V. bennetti'').

Diet

Mariana monitors in the Southern Mariana Islands shifted major prey classes when their regular prey began declining. The monitors were known for eating

shrews Shrews (family Soricidae) are small mole-like mammals classified in the order Eulipotyphla. True shrews are not to be confused with treeshrews, otter shrews, elephant shrews, West Indies shrews, or marsupial shrews, which belong to different ...

on Guam, but 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 islands ...

(''Boiga irregularis'') led to decreased shrew numbers, prompting the monitors to switch to eating invertebrates and foraging through human garbage.

Reproduction

The species lacks distinct

sexual dimorphism Sexual dimorphism is the condition where the sexes of the same animal and/or plant species exhibit different morphological characteristics, particularly characteristics not directly involved in reproduction. The condition occurs in most ani ...

, but mature male monitors on

have been reported to be three times the mass of mature females.

Relationship with humans

An ethnic group on Guam eats the monitors as a

traditional food Traditional foods are foods and dishes that are passed on through generations or which have been consumed for many generations. Traditional foods and dishes are traditional in nature, and may have a historic precedent in a national dish, region ...

, and a business there sells monitors for food. The

United States Department of Agriculture The United States Department of Agriculture (USDA) is the United States federal executive departments, federal executive department responsible for developing and executing federal laws related to farming, forestry, rural economic development, ...

’s Animal and Plant Inspection Service announced it will use a combination of two poisons,

diphacinone Diphenadione is a vitamin K antagonist that has anticoagulant effects and is used as a rodenticide against rats, mice, voles, ground squirrels and other rodents. The chemical compound is an anti-coagulant with active half-life longer than warfar ...

and

brodifacoum Brodifacoum is a highly lethal 4-hydroxycoumarin vitamin K antagonist anticoagulant poison. In recent years, it has become one of the world's most widely used pesticides. It is typically used as a rodenticide, but is also used to control larger p ...

, to kill off the rodents on

Cocos Island (Guam) Cocos Island ( ch, Islan Dåno) is an island off the southern tip of the United States territory of Guam, located within the Merizo Barrier Reef, part of the municipality of Merizo. The island is uninhabited, long in a southwest-northeast di ...

. They will also attempt to lower the mangrove monitor population on Cocos Island by 80%, using several trapping methods proposed by herpetologist Seamus Ehrhard, as the lizard is believed to prey upon the endangered

Guam rail The Guam rail (''Hypotaenidia owstoni'') is a species of flightless bird, endemic to the United States territory of Guam, where it is known locally as the ''Ko'ko bird. The Guam rail disappeared from southern Guam in the early 1970s and was ext ...

(''Gallirallus owstoni''). Most locals, however, do not see the monitor as an

invasive species An invasive species otherwise known as an alien is an introduced organism that becomes overpopulated and harms its new environment. Although most introduced species are neutral or beneficial with respect to other species, invasive species ad ...

and a few activists are opposed to the attempt to lower the population there. This has been further supported by studies showing monitors to be native to Guam.

References

{{Taxonbar, from=Q3554677 Varanus Reptiles described in 1929 Taxa named by Kyukichi Kishida Fauna of the Northern Mariana Islands Fauna of Guam