Argus monitor
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Argus monitor ( Varanus panoptes ) |
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| Storr , 1980 |
The Argus monitor ( Varanus panoptes ) is a species of the scale crawfish (Squamata) from the genus of monitor lizards ( Varanus ). This monitor, up to 1.6 m long, lives in Australia and New Guinea and is a generalist carnivore. There are three subspecies. The Argus monitor suffered a decline in populations mainly due to the advance of the invasive Aga toad ( Bufo marinus ).
features
The Argus monitor is a rather large monitor, the largest males reach a total length of 1.6 m with a weight of 7 kg. In terms of size, there is a pronounced sexual dimorphism : the females reach a total length of only about 1 m with a weight of mostly 1.5, rarely more than 2 kg. The tail length is about 1.4 times the head-trunk length in both sexes . Argus monitor lizards are quite sturdy and have a tail that is compressed to the side. The body is dark red-brown to dark gray or black, and is marked with small yellow spots and dark dots, which are arranged in bands. There are pale yellow, horizontal stripes on the head. The dot drawings extend to the sides of the abdomen and throat.
The Argus monitor looks very similar to the Gould's monitor ( Varanus gouldii ), and the two species are often confused. In general, the Argus monitor is much more robust and heavier than the Goulds monitor. In addition, the subspecies of the Argus monitor V. p. Panoptic dark horizontal stripes around its rear, lightly colored tail end, while the Gould's monitor lizard has no such banding of the last third of its tail. In addition, Gould's monitor lizards have no large, dark spots on their backs.
According to Christian (2004), behavior towards people can also be used to determine this: While the Gould's monitor lizard usually runs quickly to any nearby hiding place when confronted with a person, the Argus monitor either shows aggressive defensive behavior or runs a long way to his ancestral shelter. Trapped in a sack, the Goulds monitor remains passive, while the Argus monitor reacts with fidgeting or hissing sounds when pushed.
distribution and habitat
The species inhabits the northern parts of Western Australia , the Northern Territory , Queensland and southern New Guinea . The argus monitor lives in a wide variety of habitats, such as wetlands and rivers, but also regions near the coast, savannas, forests, mangroves and urban areas.
Subspecies
Three subspecies are currently recognized by the Argus monitor:
- V. p. panoptes : The nominate form inhabits the extreme northeast of Western Australia, the northern Northern Territory and, except for the extreme south, all of Queensland. The rear third of the tail is pale in color and with dark stripes.
- V. p. horni : Southern New Guinea, Torres Strait .
- V. p. rubidus : Western Australia, from Pilbara in the north to the south to Fields Find and Mount Linden . Also Dolphin Island and Dampier Archipelago . The subspecies is reddish in color and has no transverse bands around the back third of the tail.
Way of life
behavior
Like all monitor lizards, the Argus monitor is also diurnal. During the night he retreats to a building he dug himself. The species is mostly ground-dwelling, but can also climb, albeit more awkwardly than other species. Argus monitors are good swimmers and occasionally hunt in shallow water. In forests and dry areas the monitor lizards bury themselves at the beginning of the dry season and last for 4–5 months, ie until the next rain, a period of rest. In wetlands they remain active until the last water has dried up, as the prey then concentrates on the remaining water and is easier to catch. They only bury themselves at the end of the dry season. The Argus monitor is active all year round in permanent waters.
Even if the Argus monitor is a rather passive thermoregulator , it occasionally shows typical sun behavior and, due to the comparatively good heat absorption properties of its skin, reaches an average body temperature of 36.4 ° C during the day. After observations on the Daly River in the Northern Territory, the species basks in the sun early in the morning and looks for food in the late morning, then either foraging in shady areas or retreating into its burrows at lunchtime. Later the Argus monitor becomes active again and finally retreats into its burrow in the evening.
nutrition
In general, this monitor lizard eats everything it can overwhelm, both various invertebrates (e.g. insects) and vertebrates (e.g. lizards, small mammals, fish) as well as eggs and carrion. Particularly unusual prey animals mentioned in the literature include: a. Frilled lizards ( Chlamydosaurus kingii ), death adders ( Acanthophis antarcticus ), araura warthog snakes ( Acrochordus arafurae ) and a Goulds monitor, which weighed about 11% of the body mass of the argus monitor. The Argus monitor also occasionally invades chicken coops, where it preyes on the birds and their eggs. For the population at Fog Bay (Northern Territory), the eggs of various sea turtles are an important food source during the dry season .
The Arguswaran is an active chase who tracks down prey with its apparently extraordinarily good sense of smell. According to studies carried out in the 1990s on Argus monitor lizards living in bodies of water, the lizards search for food on an approximately 2 km long section of the river during the dry season. On average, the lizards run 3.5 hours a day, a maximum of 6.6 hours, and are therefore very active. In the rainy season they only move about 1 hour a day as food is abundant. The Argus monitor is known for digging up prey from the earth, such as the dry season surviving Goulds monitor lizards and turtle eggs. This also speaks for his exceptionally developed sense of smell. According to observations in Queensland, the Argus monitor also dives for up to 10 minutes to hunt freshwater clams.
Reproduction
Information on reproduction in the wild is sparse. According to Shea & Sadlier (2001), the eggs are laid in April and the young hatch in October. A clutch consists of 6-14 eggs. On the other hand, there were reports of a clutch near Darwin that was apparently laid in December; the young hatched in July. The pups in this clutch had a head-trunk length of 12-13 cm and weighed 27.7-32.2 g.
Occasionally found common nesting sites where the females nest in high density are striking. On 25–60 m² there are 10–20 burrows with eggs. The behavior at these nesting sites has not been adequately researched.
Argus monitors living in captivity are known to be able to reproduce parthenogenetically .
Systematics
The first description of Varanus panoptes was made in 1980 by Glenn Storr , initially the two subspecies p V.. panoptes and V. p. rubidus performed. In 1988 Wolfgang Böhme described V. p. horni . He also discovered in 1991 that a lectotype of V. gouldii was actually a V. panoptes . The separation between the two species was retained, however, and the lectotype was declared invalid.
Danger
Long-term observations on the Daly River in the Northern Territory have shown that the highly poisonous toad ( Bufo marinus ), naturalized in Australia, have a dramatic effect on the population of the Argus monitor. Cane toads originally come from South America and were released in Australia in 1935 as a biological measure against sugar cane pests (see Cane toad: Effects on the fauna of Australia ). Monitor lizards that eat cane toads or put in their mouths die from the amphibian's skin poison. The cane toads reached the Daly River in 2003; Compared to the Mitchell monitor lizards ( Varanus mitchelli ) and Australian water monitor lizards ( Varanus mertensi ) also observed on the Daly River , the population of the Argus monitor fell particularly rapidly and dramatically. Based on the frequency of sightings of Argus monitor lizards during individual inspection rounds, it was concluded that the population would decrease by 77–90% immediately after the toads arrived. In other areas, too, population declines of around 90% were recorded.
Web links
supporting documents
- ↑ a b c d e f g h i j K. Christian (2004): Varanus panoptes . In: ER Pianka & DR King (Eds.): Varanoid Lizards of the World : 423-429. Indiana University Press, Bloomington & Indianapolis. ISBN 0253343666
- ^ A b c d S. Wilson & G. Swan (2010): A complete guide to reptiles of Australia : 396 & 398. New Holland Publishers, Sydney, Auckland, London, Cape Town (3rd ed.). ISBN 9781877069765
- ^ G. Thompson (2004): Varanus gouldii . In: ER Pianka & DR King (Eds.): Varanoid Lizards of the World : 380-400. Indiana University Press, Bloomington & Indianapolis. ISBN 0253343666
- ↑ Varanus panoptes in The Reptile Database ; Retrieved January 30, 2011.
- ↑ a b J.S. Doody et al. (2007): A Preliminary Assessment of the Impacts of Invasive Cane toads (Bufo marinus) on Three Species of Varanid Lizards in Australia . Mertensiella 16 ( Advances in Monitor Research III ): 218-227
- ^ R. Shannon (2008): Observations on Three Species of Varanus in Ilfracombe, Queensland . Biawak 2 (2): 80-86 ( full text )
- ↑ SJ Blamires (2004): Habitat Preferences of Coastal Goannas (Varanus panoptes): Are They exploiters of Sea Turtle Nests at Fog Bay, Australia? . Copeia 2004 (2): 370-377
- ^ R. Shannon & RW Mendyk (2009): Aquatic Foraging Behavior and Freshwater Mussel (Velesunio sp.) Predation by Varanus panoptes panoptes in Central-Western Queensland . Biawak 3 (3): 85-87 ( full text ; PDF; 1.9 MB)
- ↑ P. Lenk et al. (2005): A parthenogenetic Varanus . Amphibia-Reptilia 26 (4) :. 507-514
- ↑ R. Wiechmann (2011): Own observations on parthenogenesis in monitor lizards . elaphe 19 (1): 55-61
- ↑ B. Ujvari & T. Madsen (2009): Increased mortality of naive varanid lizards after the invasion of non-native cane toads (Bufo marinus) . Herpetological Conservation and Biology 4 (2): 248-251