Wednesday, 20 July 2011

Nile Monitor Lizards: Invasive Species in Florida Threatens Native Species (Via Herp Digest)

0Nile Monitor Lizards: Invasive Species in Florida Threatens Native Species
Author: David R. Wetzel, Ph.D. : Posted to Decoded Science on July 13, 2011 at 6:34 pm

The Nile Monitor (Varanus niloticus) is one of the many non-native invasive species plaguing Florida. These reptiles are a serious threat to native animal species in all state habitats. The first of these aggressive and powerful lizards was found in the wild in 1981, followed by the discovery of an established (breeding) population in 1990. Since then, their numbers in the wild have been increasing steadily throughout the state.

Introduction of Nile Monitors to Florida Habitats
Nile Monitors were originally brought to this country from their native habitats in southern and central Africa as part of the exotic pet trade. Their introduction into the wild is most likely due to escapes or intentional releases by owners who could no longer handle them. These big semi-aquatic lizards may grow to over seven feet (2.42 meters) in length and weigh as much as 20 pounds (10 kg).

The increase in wild population of this invasive species is primarily a result of females laying as many as 60 eggs at a time. Eggs are laid in sand or dirt nests located near water. A female abandons the nest after depositing her eggs, relying on sunlight to incubate the eggs. Gestation typically takes four to six months.

When babies hatch, normally during the months of February through April, they immediately head for the protection of water near the nest. The apparent successful reproduction rate of this invasive species has increased the number of sightings and captures of Nile Monitors in Florida over the past 10 years.

Why These Intelligent Reptiles are a Problem
These intelligent lizards create a problem for native species because their diet includes invertebrates, endangered burrowing owls, insects, carrion, fish, young alligators, young American crocodiles, snakes, turtles, and any terrestrial or aquatic vertebrate they can overpower. They are especially a threat to native egg-laying animals such as birds, turtles, and alligators. Nile Monitors dietary preference is a nest filled with eggs or new born young.

Known for their sharp teeth and bad tempers, Nile Monitors are excellent swimmers and are not limited to any specific habitat. Their known range extends from the Florida Keys to the northern portions of the state. They are found in the Everglades, Cape Coral, Sanibel Island, Tampa Bay, and Key Largo

The range of this invasive species is likely to expand beyond Florida's borders, because these reptiles hibernate during cold months. The limit of their range is unknown; however, their ability to adapt to most habitats may extend their range into bordering southeastern states.

Controlling Non-Native Nile Monitor Lizards in Florida
The first step for controlling the wild population of Nile Monitor lizards is for owners, especially those who can no longer care for their exotic pet, to be responsible. If they are unable to find someone willing to accept their lizard, then contact the Florida Fish and Wildlife Commission. This state organization has non-native pet amnesty days and accepts any exotic pet without questions. Owners need to remember that releasing any exotic pet into the wild is illegal.

Residents need to report any sightings of these reptiles to their local Fish and Wildlife Commission office. These lizards are aggressive and may pose a threat to small children, pets, and feral cats after their escape or release into the wild. Their burrows are typically located along the shore line of canals, streams in urban areas, and golf course ponds. This invasive species is often seen basking in the sun near swimming pools, roofs, ponds, canals, sea walls, and grassy areas.

In an effort to eradicate Nile Monitors, the National Wildlife Research Center (NWRC) is investigating methods to control the spread of this invasive species capable of eating anything animal it can overpower and fit in its mouth. The NWRC is experimenting with Acetaminophen laced dead neonatal mouse and quail chicks as oral toxicant bait. Initial testing points to possible successful eradication efforts using these baits.

Residents should never attempt to capture a Nile Monitor lizard. When cornered they typically rear-up on their hind legs lashing out with sharp teeth, claws, and a strong tail. Their saliva is known to carry potentially lethal germs and pathogens, which may be fatal to humans. If bitten, seek medical attention immediately.

Campbell, T. [S.] 2003. Species profile: Nile monitors (Varanus niloticus) in Florida. Iguana 10(4):119-120

Enge, K. M., et al. 2004. Status of the Nile monitor (Varanus niloticus) in Southwestern Florida. Southeastern Naturalist 3:571-582

National Park Service and the Florida Fish and Wildlife Conservation Commission. Florida Invaders. Accessed July, 2011.

Somma. L. 2011. Varanus niloticus Fact Sheet. USGS Non-indigenous Aquatic Species Database, Gainesville, FL. Accessed July, 2011.

McGrath, S. 2005. Attack of the alien invaders. National Geographic 207(3):92-117.

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