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Spotlight / Biology Prof Publishes Book on Giant Anaconda Snakes in the Wild

​Las Vegas, N.M. – A Highlands University biology professor’s book is the first comprehensive study in the wild of anacondas, the largest snake in the world.

Jesús Rivas published Natural History of the Green Anaconda: With Emphasis on its Reproductive Biology in 2016. His study area is in the Venezuelan Llanos – a vast plain that floods during the wet season from May through October.

“My biggest goal with publishing this book is to share the knowledge with other anaconda scientists and hopefully be a catalyst for more anaconda research,” Rivas said. “Anacondas are part of one of the most diverse ecosystems in the world and are in peril. Understanding the dynamic function of the ecosystem is critical for both its conservation and anaconda preservation.”

Rivas is a Venezuelan-born herpetologist – a scientist who studies reptiles and amphibians. His anaconda research spans 24 years. He founded the ongoing Anaconda Project in 1992, which focuses on research and conservation. Rivas is also known for being featured in anaconda documentaries broadcast on National Geographic, Discovery and the BBC.

“I like to study all animals, but anacondas are awesome. Humans are fascinated by large predators so anacondas have enjoyed a place of mystery with people who inhabit the same area. They call the largest anacondas Madre de Aguas – Mother of the Waters – and believe they are enchanted and must be protected,” Rivas said.

His 183-page book is based on his 2000 doctoral dissertation at the University of Tennessee. Anacondas are nonvenomous snakes that use constriction to kill their prey.

“Anacondas live in swamps so you need to find the animals in their natural habitat in order to study them. You find them by walking through miles of swamp with water up to your knees. When you find an anaconda, you hold it behind its head and restrain it until it tires. Because of its metabolism, anacondas tire quickly in about 10 to 15 minutes,” Rivas said.

He said that unlike other species, tranquilizers cannot be used safely with anacondas because this method of capture can harm the giant snakes. In his dissertation study, the largest anaconda weighed 220 pounds and the longest measured 18 feet in length.

After capturing the snakes, Rivas took them to a dry land field laboratory to collect data such as measurements of weight and length, sex and markings. He said a small microchip was implanted in each snake so it could be identified when it was released into the wild and then caught again.

The snake’s reproduction is a primary focus of Rivas’ book.

“Male and female anacondas are very different sizes ­– called sexual size dimorphism – with the females being much larger than the males. The larger the females, the more babies it can have. The range in this study was for six babies per pregnancy weighing about 0.3 pounds per snake to 96 babies per pregnancy weighing about 0.7 pounds per snake,” Rivas said.

He said that the larger the baby anaconda, the better its survival rate in the wild – primarily because it has fewer predators.

Since joining the Highlands faculty in 2010, Rivas and fellow biology professor Sarah Corey-Rivas have led their students on several research expeditions deep into the Venezuelan Llanos to study anacondas and other tropical wildlife.

“This book is also a teaching tool for my students,” Rivas said.

In New Mexico, Rivas and his students study species of concern such as the northern New Mexico leopard frog.

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