Complex social behaviours
Iguanas have evolved behaviours far beyond the perceived limitations of the reptilian brain
Historically, it was thought that ‘complex’ social behaviours were confined to mammals and birds, but recent studies have found that sophisticated interactions such as play, parental care and co-operation are found within many reptile groups, including the Iguanidae family.
Green iguanas have been documented practising pair-bonding and kin recognition, with juveniles often defending their siblings. When threatened, the green iguana will bob its head, puff up its body and extend its dewlap, which sits beneath the jaw, to appear more intimidating. However, this doesn’t always work. Iguanas are frequently hunted by predatory birds, and unfortunately for the iguana, the sound of a hawk’s whistle or scream can make the iguana freeze, rendering it easier to capture.
Green iguanas are particularly social during the breeding season, when they adopt a lekstyle display as seen in birds of paradise. Males seek out a platform in the trees around which the vegetation is sparse, allowing maximum visibility to any passing females. Here, they will bob their heads while moving across the platform, demonstrating their large dewlap as they go. Any approaching males will be chased out of the territory, while as many as eight females can congregate around the displaying male. Those who are interested will compete among themselves to lay claim to their mate.
Green iguana females can nest in isolation, while others have been known to travel great distances in order to nest upon an island as part of a colony. In such examples, nesting is achieved by digging burrows that can cross over and interlock, growing in complexity with each year that passes. The females will guard their burrow site in order to prevent their eggs being dug up by other nesting females before leaving the brood to hatch on their own.
Most iguanas spend their life on land in arboreal habitats, and they are known to some as the ‘chicken of the trees’ due to the similarity of their meat. However, the Iguanidae family also contains the only extant oceandwelling lizard, the marine iguana, which exists exclusively on the Galápagos Islands. Marine iguanas also perform in leks during the breeding season, but on rocks rather than in trees, and they are known to stay close to their mate following copulation. It’s thought this guarding is an attempt to prevent the female from mating with another male, meaning competition between sperm doesn’t occur.
Male iguanas are very territorial and the strongest will protect their patch from competing males. Despite this, smaller males are still in with a chance as they can sneak past, undetected due to their morphological similarities to a female iguana. After the female has mated and is ready to lay her eggs, much like the green iguana she will seek out a soft, often sandy area within which to dig a burrow. Despite their aquatic nature, marine iguanas must nest on land as their eggs would drown in an underwater burrow.
“Green iguanas have been documented practising pairbonding and kin recognition”