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Varanus salvadoriiCrocodile Monitor

By Gregory Wojtasek

Geographic Range

Papuan monitors are endemic to the island of New Guinea, both Papua New Guinea and West Papua (Indonesia). (Horn, et al., 2007)

Habitat

Papuan monitors primarily reside in coastal lowland environments, mainly tropical rainforests and mangrove swamplands. Though they are typically found from sea level to 200 meters above sea level, these animals may be found in mountains up to 650 meters above sea level. They live in arboreal and terrestrial habitats, depending on availability of sunlight and prey. Since this species resides in rainforests, its optimal temperatures are high, from 29-31ºC during the day. (Horn, et al., 2007; Pattiselanno, et al., 2007)

  • Range elevation
    0 to 650 m
    0.00 to 2132.55 ft

Physical Description

Papuan monitors are the largest known species of monitor lizard found on New Guinea, growing up to 2.5 m, with an average weight of 20 kg. They have long tails, typically twice their SVL (snout-vent length), which are rounded at the base and triangular distally. The skin is covered with non-overlapping scales, and body color is mostly black with specks of yellow, white, or green, with folds around the neck. They have round snouts with long, forked tongues used for chemoreception, and very long, vertical teeth, as well as strong claws. Males are generally larger than females, due to reproductive energy expenditures by femmales. (Horn, et al., 2007; Pattiselanno, et al., 2007; Pianka, et al., 2004; "Crocodile Monitor", 2011; Wilson, 2012)

  • Sexual Dimorphism
  • male larger
  • Range mass
    90 (high) kg
    198.24 (high) lb
  • Range length
    2 to 5 m
    6.56 to 16.40 ft
  • Average length
    3 m
    9.84 ft

Development

There is no data regarding mating behavior or development of this species in the wild, but it has been studied in captivity. Egg clutches of 4-12 eggs are laid between August and January in a well-hidden hole (dug by the female). Most eggs are infertile in captivity; only four fertile clutches have been documented. Humidity and oxygen levels (altitude) appear to be important factors in egg development. Weight and dimension of eggs, as well as hatchlings, is widely variable (47-68 g and 42-49 cm, respectively); the reason for this is unknown. (Frydlova and Frynta, 2010; Pianka, et al., 2004; "Crocodile Monitor", 2011; Shine, et al., 1996; Trout, 2007)

Reproduction

Male Papuan monitors are aggressive, fighting (as all vanarids do) in a ritualized fashion that involves head weaving, bipedal clinching and wrestling in order to attract females; the larger a male is, the more likely he is to succeed. After combat, males will proceed in courting the female (by licking, stroking and scratching in other varnids), followed by a forceful act of mating, with the male biting the female's neck, resulting in bleeding wounds called mating marks. The female will then either comply, lifting her tail to allow the male to insert his hemipenes (one at a time, though both are used in one mating) or flip over in order to make copulation more difficult, if not impossible. Generally, female vanarids may mate with one or several males over a period of a few days. (Frydlova and Frynta, 2010; King and Green, 1993; Pianka, et al., 2004; Shine, et al., 1996; Wilson, 2012)

Breeding season is unknown and this behavior has not been observed in the wild. In captivity, when a male is introduced to a female, copulation nearly always takes place and eggs result. In general, varanids may lay more than one clutch of eggs per year and captive clutches of Papuan monitors typically have 4-12 eggs (although the majority of these in captivity are infertile). Size of the female seems to be linked to clutch size, with larger females producing more eggs. In captivity, eggs laying has been observed 3-4 months after copulation, with hatching taking place 20 or so days later. Male and female Papuan monitors experience varied growth patterns that illustrate this species' level of sexual dimorphism. Upon reaching sexual maturity (within 2 years of hatching), males continue to grow, whereas growth of female individuals is halted, with energy being diverted to egg production. (Frydlova and Frynta, 2010; Shine, et al., 1996; Trout, 2007; Wilson, 2012)

  • Breeding interval
    Female vanarids may lay multiple egg clutches in a year.
  • Breeding season
    Breeding season is unknown for this species.
  • Range number of offspring
    4 to 36
  • Average number of offspring
    8
  • Range gestation period
    3 to 4 months

Little is known about parental involvement of Papuan monitors after eggs have been laid. Following copulation, captive females have been noted to bury their eggs, digging holes and then filling them in such that the nests are barely visible. (Frydlova and Frynta, 2010; Trout, 2007)

Lifespan/Longevity

Lifespan of Papuan monitors in the wild is unknown. In captivity, they are known to survive for 12-20 years. ("Crocodile Monitor", 2011)

  • Typical lifespan
    Status: wild
    12 to 20 years

Behavior

Papuan monitors bask in the sun throughout the day. They are temperature sensitive and, when their body temperature exceeds temperatures of around 38ºC, body contractions aid in lowering body temperature. They are extremely agile, using their long tails to aid in balance as they jump amongst branches, and use contractions of their throat muscles to pump oxygen into their lungs when they need to move quickly and suddenly. They are known to exhibit a warning posture, in which they carry their tails rolled up behind them. (Pattiselanno, et al., 2007; Pianka, et al., 2004; "Crocodile Monitor", 2011)

Home Range

No information has been recorded on the home range of Papuan monitors due to the lack of observation in the wild. A closely related species, Varanus komodoensis, has been observed to have a home range of 2-3 km^2. (Turner, et al., 1969)

Communication and Perception

In general, varanids are known have well-developed auditory and visual systems. The tongue aids in chemoreception and olfaction, bringing air into the mouth and pressing it up against the large Jacobson's organ, which contains specialized chemoreceptors. This aids them in detecting food sources. Papuan monitors communicate with each other visually (movements such as head weaving during combat), through touch (during courtship behavior), and sound, hissing for short periods throughout a broad frequency span as a warning. (King and Green, 1993; Wilson, 2012)

Food Habits

Papuan monitors are carnivorous, feeding on small animals. They are known to prey on both adult birds and their eggs (particularly Cacatua sp. and maleos (Macrocephalon maleo)). They are also known to eat small mammals (such as rodents), reptiles and amphibians, and insects, as well as carrion. They have long, sharp teeth and powerful jaws, and are known to swallow food items whole. Unlike many other varanids, they do not appear to adjust the ferocity of their attack based on prey size. (Murphy, 2007; Pattiselanno, et al., 2007; Pianka, et al., 2004; Shine, et al., 1996)

  • Animal Foods
  • birds
  • mammals
  • amphibians
  • reptiles
  • eggs
  • carrion
  • insects

Predation

Little is known about possible predators of Papuan monitors. As they are thought to be top predators in their habitat, humans likely pose the only regular danger to these lizards, due to deforestation and the value placed upon their skins. (Horn, et al., 2007; Shine, et al., 1996; Wilson, 2012)

Ecosystem Roles

Papuan monitors are large, powerful creatures that are the dominant predators in their ecosystem, with no known predators besides humans. They are predators of many smaller animals and their eggs, controlling the populations of these organisms. Wild caught Papuan monitors have been found to be infected with enteric parasites. (Pattiselanno, et al., 2007; Pianka, et al., 2004)

Commensal/Parasitic Species
  • Cestodes (Class Cestoda, Phylum Platyhelminthes)
  • Mites (Class Arachnida, Phylum Arthropoda)
  • Oxyurids (Subclass Spiruria, Phylum Nematoda)
  • Strongyles (Order Rhabditida, Phylum Nematoda)

Economic Importance for Humans: Positive

Papuan monitors have been utilized by natives of the island for their meat and skin, which is important as clothing and as heads for ritual drums. They are not often actively hunted, due to the inherent risks associated with finding and killing these large animals, but are often caught in traps intended for other animals. (Pattiselanno, et al., 2007; Shine, et al., 1996)

  • Positive Impacts
  • food
  • body parts are source of valuable material

Economic Importance for Humans: Negative

Many of the animals that are prey for Papuan monitors are important to island natives for food and economic purposes. Also, attacks on cattle and other livestock are not uncommon. If disturbed by humans, these lizards are capable of doing severe physical damage. (Pattiselanno, et al., 2007; Shine, et al., 1996)

  • Negative Impacts
  • injures humans
    • bites or stings

Conservation Status

This species has not been evaluated by the International Union for Conservation of Nature and Natural Resources. It is listed in Appendix II of CITES, indicating that while they are not yet considered threatened or endangered, trade of these animals must be closely controlled. ("Appendices I, II and III", 2012; IUCN, 2012)

Contributors

Gregory Wojtasek (author), The College of New Jersey, Matthew Wund (editor), The College of New Jersey, Jeremy Wright (editor), University of Michigan-Ann Arbor.

Glossary

Australian

Living in Australia, New Zealand, Tasmania, New Guinea and associated islands.

World Map

acoustic

uses sound to communicate

arboreal

Referring to an animal that lives in trees; tree-climbing.

carnivore

an animal that mainly eats meat

carrion

flesh of dead animals.

chemical

uses smells or other chemicals to communicate

diurnal
  1. active during the day, 2. lasting for one day.
female parental care

parental care is carried out by females

fertilization

union of egg and spermatozoan

food

A substance that provides both nutrients and energy to a living thing.

insectivore

An animal that eats mainly insects or spiders.

island endemic

animals that live only on an island or set of islands.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

native range

the area in which the animal is naturally found, the region in which it is endemic.

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

polygynandrous

the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.

rainforest

rainforests, both temperate and tropical, are dominated by trees often forming a closed canopy with little light reaching the ground. Epiphytes and climbing plants are also abundant. Precipitation is typically not limiting, but may be somewhat seasonal.

scavenger

an animal that mainly eats dead animals

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

solitary

lives alone

tactile

uses touch to communicate

terrestrial

Living on the ground.

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

vibrations

movements of a hard surface that are produced by animals as signals to others

visual

uses sight to communicate

References

2012. "Appendices I, II and III" (On-line). Accessed October 14, 2012 at http://www.cites.org/eng/app/appendices.php.

SeaWorld/BuschGardens. 2011. "Crocodile Monitor" (On-line). Accessed November 15, 2012 at http://www.seaworld.org/animal-info/animal-bytes/animalia/eumetazoa/coelomates/deuterostomes/chordata/craniata/reptilia/squamata/crocodile-monitor.htm.

Frydlova, P., D. Frynta. 2010. A test of Rensch's rule in varanid lizards. Biological Journal of the Linnean Society, 100: 293-306.

Horn, H., S. Sweet, K. Philipp. 2007. On the distribution of the Papuan monitor (Varanus salvadorii PETERS & DORIA, 1878) in New Guinea. Advances in Monitor Research III, 16: 25-43.

IUCN, 2012. "The IUCN Red List of Threatened Species" (On-line). Accessed October 14, 2012 at http://www.iucnredlist.org/search.

King, D., B. Green. 1993. Family Varanidae. Pp. 1-19 in C Glasby, G Ross, P Beesley, eds. Fauna of Australia: Volume 2A, Amphibia and Reptilia. Canberra, Australia: AGPS Canberra. Accessed February 26, 2013 at http://www.environment.gov.au/biodiversity/abrs/publications/fauna-of-australia/pubs/volume2a/30-fauna-2a-squamata-varanidae.pdf.

Murphy, J. 2007. Notes on Indo-Australian varanids. International Zoo Yearbook, 12: 199-202.

Pattiselanno, F., E. Rahayu, J. Wanggai. 2007. Varanus species at the Arfak Strict Nature Reserve. Biodiversitas, 8: 114-117. Accessed October 12, 2012 at http://www.papuaweb.org/dlib/jr/pattiselanno/2007a.pdf.

Pianka, E., D. King, R. King. 2004. Varanoid Lizards of the World. Bloomington, IN: Indiana University Press. Accessed February 26, 2013 at http://books.google.com/books?id=0e3OuHRRoIQC&dq=%22Varanoid+Lizards+of+the+World%22+pianka&pg=PP1&hl=en#v=onepage&q&f=false.

Shine, R., P. Harlow, J. Keogh. 1996. Commercial harvesting of giant lizards: The biology of water monitors Varanus salvator in southern Sumatra. Biological Conservation, 77: 125-134. Accessed October 12, 2012 at http://www.deepdyve.com/lp/elsevier/commercial-harvesting-of-giant-lizards-the-biology-of-water-monitors-KcT0KitrW9/1.

Trout, T. 2007. Observations of breeding and nesting behaviors in captive Varanus salvadorii. Mertensiella, 16: 441-447. Accessed February 26, 2013 at http://www.reptileranger.com/Denver%20zoo-%20Tim%20Trout%20abstract.txt.

Turner, F., R. Jennrich, J. Weintraub. 1969. Home ranges and body size of lizards. Ecology, 50: 1076-1081.

Wilson, S. 2012. Australian Lizards: A Natural History. Collingwood, VIC, Australia: CSIRO Publishing.

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