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In a Drought, Water-Starved Iguanas Will Eat Each Other to Survive

A review in Mesoamerican Herpetology suggests drought is just one of the reasons this odd behavior sometimes occurs.
A black iguana attacks a juvenile of the species in Costa Rica, August 2014. Image: Flávio H. G. Rodrigues

​If you think giving up almo​nds because of the drought in California is hard, try being an iguana. A review published in the journal Mesoamerican Herpetology suggests that when iguanas face extenuating circumstances like drought, they resort to cannibalism.

José M. Mora, a conservation researcher at the National University of Costa Rica, and colleagues looked to previous research to try to explain a case of iguana cannibalism they observed last summer. The team published their revi​ew in the most recent issue of the journal. Mora suggested reptiles only eat their own when they're really desperate, including when drought wipes out nearly all of their normal food sources.


The case the team observed occurred last August at the Guanacaste Conservation Area in Costa Rica. An adult female black iguana (Ctenosaura similis) grabbed and chowed down on a juvenile of the same species, which was about three months old. Mora explained that the new hatchlings are born in late May, which usually marks the beginning of the rainy season and food (both plants and insects) begins to become more plentiful once again. But last year's El Niño led to drought conditions so that by August, food for the iguanas was still scarce.

"Hatchling C. similis would be a good alternative food source for some adults when facing an extended dry season," Mora and the other authors wrote in the review. "(This) was the situation at Sector Santa Rosa in 2014 due to the El Niño event. Thus, adults would have taken advantage of this situation and many young individuals probably succumbed to predation."

Other research suggests cannibalism is rare in reptiles. A st​udy from Pennsylvania State University researcher Travis R. Robbins noted while cannibalism doesn't seem very beneficial from an evolutionary perspective, it can have some benefits, particularly when there are pressures from lack of food or population density. In the case of the Costa Rican iguanas, since drought conditions mean the juvenile iguanas probably wouldn't have survived anyway, resorting to cannibalism to keep the adult members of the species alive makes a little more sense, the review explained.

And there are likely a number of factors that contribute to an iguana decided to turn on one of its own. There could be a lack of food due to overpopulation, rather than environmental conditions, and cannibalism could help control the population while also providing an alternate food source. That was the case for Skyros wall lizards in Greece, where an overgrown population led to cannibalism, according to a s​tudy in Ethology

"Cannibalism could offer a number of advantages for a predator in natural populations by eliminating potential competitors, among other things," the review stated. "A moderate level of cannibalism reduces inter-cohort competition, enabling the coexistence of many cohorts , a phenomenon referred to as the 'lifeboat mechanism' because it could save a population from extinction."