Lizards do really learn to recognize people

June 30, 1999

Despite their cold-blooded demeanor, lizards can form personal relationships with people. A team of scientists has shown that iguanas recognize their human handlers and greet them differently, compared with strangers.

Scott McRobert and his colleagues at Saint Joseph's University in Philadelphia had often joked that their lab's pet iguana "Fido" would bob his head when McRobert approached but ignore everyone else. They decided to design an experiment to find out if Fido really did know his handler. They also wanted to see if the twelve-year-old lizard remembered a lab student who had cared for him four years earlier.

McRobert, the student and around forty strangers took turns reading the Dr Seuss children's book Oh, the Places You'll Go! to Fido. They read it aloud or silently, in front of Fido's cage or behind a screen, while another researcher counted the iguana's head bobs.

When Fido could see the readers but not hear them, he bobbed his head roughly equally to both the student and McRobert, but almost totally ignored the strangers. When they read aloud, however, Fido bobbed his head around three times as often to McRobert than to the student. "Visual cues alone are enough for him to recognize individuals," says McRobert, but he suspects that Fido "fine-tunes" his response with audio cues.

"I'm pretty sure that this is the first time human recognition by a lizard has been demonstrated in a scientific way," says McRobert, who described the study this week at a meeting of the Animal Behavior Society in Lewisburg, Pennsylvania. He suspects Fido singles him out because iguanas are not normally handled and see handlers as a threat: "It's not that he loves me," McRobert says.

He plans to use recorded voices to see what Fido will do when visual and audio cues don't match up. "We may actually learn something about how these animals recognize individuals."
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