Reptiliana: Ultimate Reptile Resource


White Throated Monitor – Varanus albigularis
March 1, 2008, 11:41 pm
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Scientific name: Varanus albigularis albigularis
Family: Varanidae
Order: Sauria
Class: Reptilia

PHYSICAL CHARACTERISTICS:

The White-throated Monitor has a large and muscular body, an elongated head with a dome-shaped snout, short sturdy limbs, and a strong, thick tail. The length of the tail slightly exceeds the sum of the animals head and body lengths. Furthermore, the tail functions as a prehensile organ, a rudder, and as a weapon. The front legs are surmounted with long, sharp claws that enable this lizard to dig and climb. White-throated Monitors are adept climbers. As common to all Varanidae, they have long, forked tongues. The tongue is not only used for drinking but also in a sensory capacity. It is a common myth told to tourists that the White-throated Monitor lizards suck milk from cattle udders. The adult White-throated Monitor can attain lengths up to 120 to 150 cm (4 6 ft.) from the tip of its snout to the end of its tail. The average weight of the adult male is 8 kg (17.5 lbs). The adult female has an average mass of 6.5kg (14 lbs.) In captivity, both sexes tend to become obese, weighing up to 20 kg (44 lbs). An ivory-colored throat is the distinguishing characteristic of this monitor. Its body is covered with 110 to 140 small, beadlike scales that form reticulated and banded patterns of gray, brown, and black, intermingled with conspicuous yellow and/or white patterning.

DISTRIBUTION and HABITAT:

The White-throated Monitor is found throughout Central and Southern Africa. The White-throated Monitor is both terrestrial and arboreal. It inhabits the savanna, steppe, open bush, and woodland regions. However, it is not generally found near water sources. This monitor has a large home range relative to its body size. The home ranges of males average 18.3 square kilometers (approx. 7 sq. miles), whereas the home ranges of females average 6.1 square kilometers (approx. 2.5 sq. miles). Researchers have shown that the home ranges of both sexes do indeed overlap.

BEHAVIOR:

The White-throated Monitors are essentially solitary individuals. They generally ignore each other until the mating season. These monitors are diurnal. Reproductive males and females will fully utilize their home range foraging during the wet season. Only the males roam their home ranges during mating season, whereas the females remain in one particular location of their home range. Throughout the remainder of the year when prey populations are low to nonexistent, both sexes limit their daily movements and remain basically sedentary so as to conserve energy. It should be noted that the White-throated Monitor will not attack humans unless provoked. When threatened, the White-throated Monitor will assume an intimidating posture by arching its neck, puffing out its throat, and hissing loudly. It will then lash out with its tail and bite violently at anything within its reach. This monitor is a formidable opponent. As a last effort, it will allow itself to be attacked. When its foe leaves it for dead, this monitor is able to survive because it is able to rapidly recuperate. White-throated Monitors have been noted to fight to the death. The main competitor of the White-throated Monitor is the black-backed jackal, as both have similar diets. Predators of this monitor are ratels, birds of prey, and most large carnivores.

DIET:

The White-throated Monitor is a voracious feeder between the months of January to February, also known as the wet season. It will travel long distances in search of prey. During the dry season from July to December, it fasts losing approximately 4% of its body weight per month. Research has shown that this monitor has an adaptive relationship between its feeding habits and digestive responses similar to sit-and-wait foraging snakes. This adaptation serves to conserve energy during the long interval between meals. Its diet in the wild ranges from invertebrates, small reptiles, birds and eggs to occasionally small mammals and carrion. Land snails are the favorite prey. Studies have shown that it uses visual and chemical cues in distinguishing its prey. This monitor is a selective feeder. It seeks to obtain the highest caloric intake at the least energy expense of handling time despite the availability of other prey choices. The White-throated Monitor does not chew its food, but instead swallows small prey or large pieces of prey whole by increasing the size of its mouth. This is accomplished by spreading the hyoid apparatus and dropping the lower jaw.

REPRODUCTION and GROWTH:

White-throated Monitors are oviparous. In the wild, females will produce one clutch of up to 50 eggs. However in captivity, females will lay multiple clutches per year. During the cool, dry season from May to August, the male will go on a tour of his home range six weeks prior to mating. He will visit the locations of reproductive females. The male exhibits the same behavior patterns as when foraging. During this period, the females remain relatively stationary, preferring to remain upon elevated sites, such as trees and rocks. During this period of touring, it appears that feeding or mating does not occur. The male seems to remember the locations of the fertile females and will return to mate with them at their optimum time. During the courtship, the male will wipe his mouth on elevated objects immediately adjacent to the female and display vent dragging. He will make exaggerated, spasmodic movements as he approaches the female. The response of the female is to flatten her body and press her head down to the ground. Before actual contact, the males will flick his tongue around the females mouth, hind legs, and the base of her tail. The female remains passive during courtship and mating; therefore, there is no aggression between the sexes. White-throated Monitors prefer to copulate in trees. Intruding males will be chased away by the resident male. Researchers did not observe any ritualistic combat between males. Both sexes will mate with multiple partners. The female lays her eggs in a nest in an abandoned ground squirrel burrow. The eggs are covered and left to hatch. Egg laying usually occurs two months prior to a significant rainfall. The eggs are turgid and possess a high water content. The hatchlings emerge throughout the rainy season and feed primarily upon invertebrates. During the next three months, they will triple their mass and double in body length. In the wild, less than half of the hatchlings will survive. White-throated Monitors are reproductive at 3 – 5 years of age. Their life expectancy is about 15 years.

CONSERVATION STATUS:

This species of monitor is classified as threatened by CITES under Appendix II. The greatest threat to White-throated Monitor populations is habitat destruction and fragmentation. The native inhabitants hunt the White-throated Monitor for its alleged medicinal properties. This animal is also hunted for its hide and as a food source. This species, as well as all monitors, are sold worldwide as part of the exotic pet trade. One of the unfortunate consequences of the illegal export/import of monitors is the spread of parasites. Three species of African ticks parasitize the White-throated Monitor: Aponomma exornatum, Aponomma flavomaculatum , and Aponomma latum. These ticks are vectors of the deadly heartwater disease, which is a serious threat to domesticated animals. Recently, this disease afflicted sheep, cattle, and deer in Florida. Monitor ticks are also vectors of Coxiella burnetti, a Rickettsiales agent responsible for Q fever in humans. Q fever is characterized by fever and pneumonia-like symptoms. It is rarely fatal.

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