Life of marine iguanas on the Galapagos

The marine iguanas on the Galapagos Islands lived without predators for a very long time. But when humans arrive 150 years ago, they brought with them cats and dogs which are occasionally biting the iguanas. Still, these animals remained excessively tamed. With the explosion of the number of tourists on these protected islands, researchers from Germany and the U.S. recently to measure the levels of stress of these marine iguanas by chasing them (gently), capturing them and analyzing their blood to see how they reacted. Initially, the 'naive' iguanas didn't move until the scientists were at less than one meter from them. But the researchers were still able to 'capture the same animals up to six times in four weeks.' Maybe this is the end of the good life for these iguanas.

The marine iguanas on the Galapagos Islands lived without predators for a very long time. But when humans arrive 150 years ago, they brought with them cats and dogs which are occasionally biting the iguanas. Still, these animals remained excessively tamed. With the explosion of the number of tourists on these protected islands, researchers from Germany and the U.S. recently to measure the levels of stress of these marine iguanas by chasing them (gently), capturing them and analyzing their blood to see how they reacted. Initially, the 'naive' iguanas didn't move until the scientists were at less than one meter from them. But the researchers were still able to 'capture the same animals up to six times in four weeks.' Maybe this is the end of the good life for these iguanas.

Here is a brief description of the experiments.

The researchers conducted so-called "harassment experiments". At first, they recorded the original flight initiation distance of "naïve" animals. The researchers then experimentally chased the animals for 15 minutes, always approaching up to the point where the reptiles moved away and fled a short distance. At the end of the experiment, the scientists captured the animals and collected blood samples in order to determine CORT levels. When animals interpreted the situation as threatening, the concentration of corticosteroid hormones in the blood plasma increased within just a few minutes.

But don't worry: not a single iguana was hurt.

Thomas Rödl, from Princeton University and the Max Planck Institute for Ornithology, has assembled a page about his research projects. He wrote that "the Marine iguana [see below] is a good model to investigate the relationship between the stress response and potential fitness benefits, because individuals vary largely in body size, body condition, and social status." (Credit: Thomas Rödl)

A marine iguana on the Galapagos

Land iguanas are even more fearless. Back in 2003, Rödl and his colleagues already visited the Galapagos Islands and told what they did in "Excursion to the Imps of Darkness" (MaxPlanckResearch Magazine 2/2003, (PDF format, 6 pages, 10.2 MB)). As the article says, "land iguanas are regular visitors to the camp. Nothing is safe from them. These iguanas, reaching five kilograms in weight, will investigate everything: from compost buckets to dirty pans." As you can see below, this particular one seems to enjoy what the chef prepared.

A land iguana on the Galapagos

If the iguanas are not really afraid by humans, what can be their future?

In 2005, approx. 126,000 people descended on the island, and the trend is rising. And this causes problems. Not only do tourists disturb the many animals living on the Galápagos Islands; they also introduce alien animal and plant species which are causing great damage to local flora and fauna.
For in the meantime, the government of Ecuador has opened the UNESCO world heritage site of the Galápagos Islands to the cruise ship market. With growing mass tourism, the situation is getting more difficult. The National Park Management is considering raising the entry fee from the currently charged $100 to $500 in order to reduce the number of visitors - possibly the only possibility to create sustainable tourism, thereby ensuring the necessary protection of the unique animal and plant world of the Galápagos.

So will these iguanas survive? Time will tell.

For more information, this research work has been published in the Proceedings of the Royal Society B: Biological Sciences under the title "Tameness and stress physiology in a predator-naive island species confronted with novel predation threat" (Publication online: November 28, 2006). Here are two links to the abstract and to the full paper (PDF format, 6 pages, 254 KB, available from the abstract if the direct link doesn't work).

Sources: Max Planck Society press release, December 18, 2006; and various websites

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