Heavy Tourist Feeding Leads to Nutrition Imbalance in Bahamian Rock Iguanas

The physiology of rock iguanas inhabiting heavily touristed islands in the Bahamas is markedly different compared to iguanas of the same species found on less-visited islands, which researchers suggest is directly linked to tourists feeding the reptiles.

Rock iguanas, which are listed as critically endangered on the IUCN Red List of Threatened Species, due to habitat loss, illegal hunting and introduced species, may face additional threats from humans feeding them, the researchers report in the journal Conservation Physiology.

Both male and female rock iguanas living on islands frequently visited by tourists showed notably different levels of glucose, uric acid and potassium in blood and fecal samples. Furthermore, male rock iguanas found in tourist areas displayed differing levels of calcium, cholesterol, cobalt, copper, magnesium, packed cell volume, selenium, and triglycide concentrations, and females in the same areas differed significantly in ionized calcium, the researchers found.

Both males and females in these areas has atypically loose feces as well as a 100 percent endoparasitic infection rate.

"Both sexes on visited islands consume food distributed by tourists, although male iguanas are more aggressive when feeding and eat more provisioned food," said Charles Knapp of the John G. Shedd Aquarium in Chicago. "Consequently, they may be more impacted by provisioning with unnatural foods, which could explain the greater suite of significant physiological differences in males between populations."

These fed iguanas commonly eat grapes that are distributed by tour operators on a daily basis, the researchers said. Being fed too many sugary fruits may contribute to the generally higher average glucose levels of the iguanas on tourist islands. Additionally, grapes are low in potassium, with as much as 10 times less potassium than some of the native plants on the islands. A grape-heavy diet may be contributing to these lower levels, the researchers said.

Higher cholesterol levels in the iguanas also suggests that meat has been introduced into their diet.

"The biological effects of altered biochemical concentrations may not be manifested over a short time period, but could have deleterious effects on long-term fitness and population stability," Knapp said.

While tourist-feeding does result in an arguably more beneficial iguana population density, the researchers warn that unnaturally high density, couples with an increasing reliance on tourists for food may prove to be problematic if the food supplementation were to suddenly be discontinued.

"The complete restriction of feeding by tourists may not be a realistic option. Instead, wildlife managers could approach manufacturers of pelleted iguana foods and request specially-formulated food to mitigate the impact of unhealthy food. Tour operators could offer or sell such pellets to their clients, which would provide a more nutritionally balanced diet and reduce non-selective ingestion of sand on wet fruit," Knapp said.

"We also endorse a broad education campaign and discourage references to feeding iguanas on advertisements. We urge serious discussions among wildlife managers and stakeholders to identify tactics that mitigate the impacts of current tourism practices without compromising an important economic activity," Knapp said.