Galapagos marine iguanas react to mockingbirds’ alarm calls

This video is about birds in the Galapagos islands: ‘Flamingoes, yellow-crowned night heron, oystercatcher, lava heron, Hood mockingbird, cactus finch, great blue heron, brown pelican, short-eared owl’.

From New Scientist:

Eavesdropping iguanas heed hawk alarms

04 October 2007

Roxanne Khamsi

Galápagos iguanas may not be able to communicate amongst themselves, but it seems they can still catch the drift of mockingbird conversations. A new study shows that the island lizards – needfully wary of predators – often run to a sheltered location upon hearing alarm calls produced by mockingbirds.

Researchers say that eavesdropping must offer a huge survival advantage to the iguanas, who cannot pass warnings between themselves.

Ecologist Maren Vitousek at Princeton University in New Jersey, US, who carried out the study, adds that the finding “suggests that the transfer of information [between] species may be a much more widespread phenomenon than was previously assumed”.

The Galápagos marine iguana (Amblyrhynchus cristatus) and Galápagos mockingbird (Nesomimus parvulus) both live in fear of ending up in the deadly clutches of the islands’ hawks. However, while mockingbirds chirp alarm calls to warn of the presence of a predator, iguanas are unable to communicate this danger to one another.

Vigilant behaviour

Vitousek and colleagues suspected that the iguanas might instead pick up on the alarm calls of mockingbirds. To test the theory, the team visited various parts of the Santa Fe Island in the Galápagos and played iguanas recordings of both mockingbird alarm calls and normal songs.

The researchers observed the response of 226 iguanas to the recordings. They saw that 48% of the animals exhibited vigilant behaviour upon hearing the alarm calls, either raising their heads to look for a predator or running to a sheltered location. By comparison, only 28% of the iguanas showed vigilant behaviour when played the mockingbird songs.

On certain parts of the island, where hawks are particularly common, as many as 70% of the lizards showed a fearful response to the alarm calls, while 40% responded the same way to ordinary songs.

Experts say finding may be the first example of a silent species eavesdropping on communications from a more vocal animal.

Eavesdropping networks

Another recent study found evidence that red-breasted nuthatches in Canada eavesdrop on chickadees in order to glean information about predators. But it remains unclear whether this is simply because the birds’ calls are similar to one another, says Chris Templeton at the University of Washington in Seattle, US.

“Here, because iguanas do not vocalize themselves, it’s pretty clear that they really associate the mockingbird alarm calls with danger from a hawk,” Templeton explains. “This study is nice evidence that other animals, even completely unrelated species, glean important information from listening to the sounds of other species.”