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Nile monitor lizard program focuses on invasive species

By Staff | Apr 6, 2011

Dee Serage-Century, SCCF's Living With Wildlife Educator, holds up a photograph of a green iguana, one of two reptile species identified as invasive by the city's Exotic Lizard Management Program.

Back in June 2008, police responded to a call of a possible dead alligator floating in an inland lake on Surf Sound Court, adjacent to the Sanibel River.

However, what responders to the scene discovered wasn’t an alligator or even a crocodile. It was a six-foot long, 40-pound Nile monitor lizard, one of the rarer reptile species to be discovered on Sanibel in many years.

Only a few months earlier, the City of Sanibel had established an Exotic Lizard Management Program to manage the green iguana (Iguana Iguana) and the Nile monitor lizard (Varanus Niloticus) population. In the first year of the program, more than 750 iguanas were removed. However, only three Nile monitor lizards were identified.

Now more than two-and-a-half years later, the city is still keeping a lookout for the invasive — but very elusive — Nile monitor lizards. Last week, the Sanibel-Captiva Conservation Foundation (SCCF) hosted an informative program about the species, discussing where the creatures originally came from, how they got here, and what can be done to keep their numbers under control.

Led by Dee Serage-Century, SCCF’s Living With Wildlife Educator, shared information about the life cycle of the lizard that can swim long distances and even climb trees.

A photograph, taken in June 2008, of the six-foot Nile monitor lizard found floating in a lake on Sanibel.

“I don’t think there’s been a sighting of a Nile monitor lizard since the one was found in 2008,” said Serage-Century. “Hopefully, the cold spell we had last winter knocked back some of that population.”

Nile monitor lizards, which are native to Africa, can reach lengths upwards of seven feet in length. These lizards usually live on vacant lots along vegetated canal banks where they can evade capture by diving into an adjacent burrow or canal. They are extremely good swimmers and may remain submerged for up to an hour.

Additionally, these lizards have a high reproductive rate and may lay as many as 84 eggs in a single clutch with the average being around 60 eggs. Their high reproductive rate coupled with a lack of predators to keep them in-check, make them a very serious threat to the island’s wildlife.

Although they look similar to the green iguana, they are easily distinguishable by their elongated head, lack of spiny crest and dorsal spines.

During last Friday’s program, Serage-Century showed a documentary film, entitled “Expedition Nile Monitor Lizard: Race Against A Reptile Invasion.” The film, made for German television, focuses on the more than 2,200 population of Nile monitor lizards in Cape Coral.

“Several times a month, biologists and volunteers have to remove uninvited visitors from gardens, garbage containers or swimming pools. The visitors are Nile monitor lizards,” the film begins. “As the name implies, these reptiles originally came from Africa. Because exotic animals are popular pets in Florida, some 20 years ago reptile dealers imported a few young animals. But no one told the buyers that these animals could grow to be over 2 meters long. Now they are a pest.”

The film, which follows Cape Coral lizard expert Conny Spurfeld, traces the tracks of the monitors back to their original habitat in East Africa, trying to find solutions for the growing lizard problem in Florida.

A major danger for Sanibel is that Nile monitor lizards are particularly fond of eggs, including those of birds and gopher tortoises and could greatly impact their populations. They also climb very well, allowing them to invade bird rookeries completely destroying their nests, and as an exotic it could interfere with the population balance of wildlife on the island.

“The Nile monitor lizard is an omnivorous predator and will readily consume almost anything that will fit in their mouth such as snails, clams, crabs, fish, amphibians, reptiles and mammals, including domestic pets,” a City of Sanibel Department of Natural Resources brochure on Exotic Lizards states, in part. “In addition, large Nile monitor lizards may also pose a threat to small infant humans if left unattended.”

Should citizens see an iguana or monitor lizard, they should immediately report their sightings to the Sanibel Police Department at 472-3111. Unless there is an imminent threat to human safety, people should not call 9-1-1.

“Since the city’s nuisance alligator program was put into place, the green iguana population has skyrocketed,” added Serage-Century. “And the only way to win the Nile monitor lizard war is to stay ahead of the game.”