About Author: Glenn Gerber

Posts by Glenn Gerber


Lizards of Guatemala

A large male Guatemalan beaded lizard relaxes in one of the outdoor breeding pens.

I was recently in Guatemala for the 15th annual meeting of the International Union for the Conservation of Nature (IUCN) Iguana Specialist Group (ISG). Thank goodness for acronyms! As the name implies, the group is focused on the conservation and preservation of iguanas. These large, herbivorous lizards are found throughout much of the New World’s tropics and subtropics. Many iguana species are threatened with extinction due to hunting (apparently they taste like chicken), habitat loss associated with agriculture and development, introduced predators, road kills, and other human-associated threats.

Part of the meeting included a workshop focused on local iguana species, one of which occurs in Guatemala’s Montagua Valley. After the meeting and workshop, the group took a field trip to this valley to see these iguanas and to visit the conservation-breeding program for one of Guatemala’s other rare and endemic species, the Guatemalan beaded lizard, a close relative of the Gila monster found in the deserts of the American Southwest.

Thanks to the efforts of local conservationists, the future for both the iguanas and beaded lizards of the Montagua Valley is looking brighter.

Glenn Gerber is head of the San Diego Zoo’s Caribbean Regional Program. Read his previous post, Iguanas: Why Move?


Iguanas: Why Move?

Turks & Caicos iguana

Late 2011 marked the first in a series of experimental iguana translocations on Big Ambergris Cay in the Caribbean’s Turks & Caicos designed to determine the conservation value of moving these large, endangered lizards out of areas slated for development to areas on the island that will not be developed. At first glance you may find it difficult to question the value of moving animals like this. Then again, why wouldn’t you move animals out of the bulldozer’s path? Well, what if the translocated animals simply return home? Or what if their survival in their new habitat is very low? Both of these outcomes are actually quite possible.

Iguanas are territorial animals with small home ranges, and they live a long time. They know their territories well and have invested a lot of time and energy establishing themselves in these areas. This means that animals moved away from their home areas may be highly motivated to return. It also means that iguanas moved to a new area may find they are not welcome by the iguanas already living in that area.

To test these ideas, we moved adult and juvenile animals of both sexes and attached radio transmitters to them to follow what they did. Five out of 12 adults moved (3 males, 2 females) successfully returned to their home areas, and all of those that didn’t return home had tried to. All of the adults moved also lost weight, an indication that they were stressed by the move.

In contrast, none of the 12 juveniles moved returned home, although some did make movements in that direction. The juveniles also lost less weight than the adults, suggesting they may be better candidates for such translocations. To determine if these conclusions are valid, we will need to repeat this experiment to increase our sample sizes. In the end, we will be able to implement a conservation management strategy that makes the best use of limited resources and has the best probability for success.

Glenn Gerber is head of the San Diego Zoo’s Caribbean Regional Program. Read his previous post, Turks Island Boas.


Turks Island Boas

Turks Island boa

It’s difficult to believe that in an environment dominated by ocean and large sharks, the apex land predator in the Turks and Caicos Islands is a small, nonvenomous snake. A really, really big Turks Island boa is 5 feet long (1.5 meters) and weighs a whopping 1 pound or so (0.4 kilograms). Most are much, much smaller, less than three feet long in fact, and weigh only a few ounces. Nonetheless, like most snakes, humans often fear these animals, and malicious killings are part of the reason they are now rare on most islands in the Caribbean Sea. Another reason is predation by introduced cats and dogs, which the boas have no fear of or natural defenses from. Human development and the habitat loss and vehicular traffic that come with it are other reasons.

The boa pictured here is a large female from Big Ambergris Cay, a small island located on the eastern edge of the Caicos Islands. Big Ambergris has the largest remaining population of this species and one of the densest-known boa populations in the world. The island is only about 2.5 square miles (6.5 square kilometers) in area, but population estimates suggest there are over 2,000 snakes there!

Unfortunately, Big Ambergris Cay is now in the process of being developed as an exclusive private resort community. The challenge ahead will be to find a balance between the needs of humans and native wildlife, like the boas. Fortunately, both the government and the developers recognize this challenge and are working with conservationist to ensure such a balance is achieved.

Glenn Gerber is head of the San Diego Zoo’s Caribbean Regional Program. Read his previous post, Boas in the Caribbean.


Boas in the Caribbean

Turks and Caicos rainbow boa

Turks and Caicos rainbow boa

In mid March, I spent nine days on Big Ambergris Cay in the Turks and Caicos Islands conducting research on the Turks and Caicos rainbow boa Epicrates chrysogaster. Of course, I wasn’t alone! I was with a team of three volunteer assistants and Graham Reynolds, a collaborator and population geneticist from the University of Tennessee. Our project, now in its second year, is focused on understanding the natural history, genetics, and population density of boas in order to formulate a comprehensive plan for their conservation and management.

Big Ambergris, a 1.5-square-mile (4-square-kilometer) private island, is undergoing extensive development and is believed to support the most abundant population of this species remaining. Fifty-nine boas were tagged in 2008, and so far 103 new boas have been tagged in 2009. Out of 165 total captures to date, only 3 have been recaptures of previously tagged individuals, suggesting the population is indeed very large and dense.

My research on boas received considerable media attention during my recent research trip as well! A film crew from the TV show Timbuktu, a popular animal documentary series in Italy, filmed the team in the field; Graham and I were interviewed about our research with boas (and iguanas) by two local TV channels in the Turks and Caicos Islands; and the Turks and Caicos Sporting Club, which manages Big Ambergris Cay, highlighted my research in a press release.

Turks and Caicos dwarf boa

Turks and Caicos dwarf boa

While working on Big Ambergris Cay in March, we also found the first specimen of the endemic Turks and Caicos dwarf boa Tropidophis greenwayi greenwayi recorded from the cay since it was described in the 1930s. Several herpetological surveys conducted in past decades failed to record the species on the cay and concluded, in error, that the species had been extirpated from the island. The snake was photographed, measured, tagged, sampled for genetics, and released. If other specimens are found, they will also be tagged so that information can be compiled on this rare and endemic species.

Glenn Gerber is head of the San Diego Zoo’s Caribbean Regional Program.

Here’s more information about Glenn’s study
Here’s more information about boas