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If you give an iguana a grape... Iguana diets tell the story of tourism

One of the many exhilarating parts of vacationing in a new place is seeing the native wildlife for the first time. If you visit The Bahamas, you may see a reptile that’s not found anywhere else in the world: the endangered Bahamian rock iguanas of the Exuma Island chain.

Feeding wildlife, including the iguanas, has become an increasingly common tourist activity that is incredibly complex, especially in countries heavily dependent on tourism revenues like The Bahamas. For better or worse, wherever you may travel, know that your actions can have long-lasting impacts, including implications for health and behavior, on the individual animal or local population.

An Exuma rock iguana rests on the warm sands of a Bahamian beach as the R/V Coral Reef II, Shedd's research vessel, waits in the ocean offshore.

Could grapes lead to iguana diabetes?

Shedd Aquarium pioneered research on rock iguanas and has continued to study species in The Bahamas for 25 years. In a recently published study, further investigating and building on the findings of prior research published in 2013, the team discovered that rock iguanas that are fed grapes by tourists experience concerning spikes in their glucose (sugar) levels in their blood. Grapes, which do not occur naturally on the islands, are higher in sugar than the rock iguana’s natural diet of predominantly native leaves, flowers and fruits.

““If these [iguanas] were humans we would be talking about diabetes…"”

Susannah S. French

“A prolonged high sugar diet can ‘exhaust’ the ability to regulate blood glucose,” said Susannah S. French of Utah State University, lead author on a recent study published in the Journal of Experimental Biology called “Glucose tolerance of iguanas is affected by high sugar diets in the lab and supplemental feeding by ecotourists in the wild.”

Although more research is needed, it’s thought that if tourists keep feeding grapes to these iguanas, they could lose the ability to effectively regulate their blood sugar.

“If these were humans we would be talking about diabetes, however, it is not yet clear what the health implications are here. That is something we are continuing to work on,” French said.

Chuck Knapp, Ph.D., Shedd’s vice president of conservation research, has been studying the basic biology of these one-of-a-kind iguanas since 1998. Knapp and seven other experts contributed to and co-authored this study, which included giving specific glucose drinks to green iguanas in a lab and rock iguanas in The Bahamas, monitoring their behavior, testing their blood glucose levels, and comparing the results.

Human foods wreak havoc with turtles, stingrays, too

Additional research on iguanas and different aquatic species near tourist destinations like juvenile green sea turtles in the Canary Islands, stingrays in Grand Cayman and others, reveals that tourists feeding an unnatural diet can cause alarming digestive problems, a range of nutritional deficiencies and elevated cholesterol levels.

Snack foods can make wildlife more aggressive

Tourists feeding and interacting with the rock iguanas have also negatively impacted their behavior. The iguanas have been conditioned to run out of the brush to the beach expecting to be fed when they hear boats approach the islands, which is potentially dangerous behavior for a wild reptile.

All of us working together—tourists, scientists, governments, the tourism industry—could mean healthy animals and communities

Through our ongoing work in The Bahamas, Shedd is committed to using what we know to further develop our relationships with local tour operators and improve conditions for the iguanas.

“Tourism is such an integral part of the country’s economy,” Knapp says. “We’re looking for outcomes that lead to sustainable animal populations but also sustainable livelihoods for the people there.”

Though the negative impacts are evident, feeding wildlife can also have beneficial effects on animals such as increasing nutrient intake during periods of low-food availability, Knapp said. Close interactions between people and wildlife through nature-based tourism can promote positive attitudes toward and support for conservation.

Knapp said since he’s been working in The Bahamas, there has already been a positive progression of tour operators responding to the teams’ findings to keep the iguanas healthy.

“We’re still in the process of finding solutions that work for the animals and the tour operators, including delivery of food and the type of food that tourists can give the iguanas.”

If you are traveling this summer or even just admiring the wildlife that visits your neighborhood, remember Bahamian rock iguanas: look, admire, but don’t feed.

Learn more about Shedd’s work to save Bahamian rock iguanas and what you can do to help: Learn more about Shedd’s work to save Bahamian rock iguanas and what you can do to help: