Interpreting Non-Breeding Behaviors in Green Iguanas
Context and Subtext
©1996 Melissa Kaplan
I often hear, "My iguana hates me!" Does the iguana really hate its owner? Does the iguana hate anything at all? Probably not. Does the iguana recognize that it can intimidate the owner? Probably. Most definitely, in many cases!
Iguanas speak a foreign language. Being able to verbalize only a harsh, guttural hiss, the balance of their communication is physical: arrangement of the body (posture), movement (stylized walking or strutting), bobbing, and use of three-dimensional space (placement; seeking height or flattening out). They have a limited vocabulary, one that, like some spoken languages, has some very subtle nuances in pronunciation. They are easily able to communicate with other iguanas in this language of the body. But, while iguanas are able to learn some spoken words or sounds that we make (such as their names, or the sound of the refrigerator door opening), they can only effectively communicate to us in the language they know best. It is up to us to learn to at least read their language, interpret their postures, movements and placements, and to learn how such movements on our part may communicate action or intent, intentional or not, on our part.
Dewlaps rigidly extended is a threatening gesture. The extended dewlap, along with the sideways presentation of the body (and the illusion of additional height afforded by the dorsal crest) makes the silhouette of the iguana larger, thus more fearsome. It is effective in warning off some predators, other iguanas venturing into their territory, and many humans.
Larger iguanas have larger dewlaps. When at rest and relaxed, the dewlap may hang down, flopping on the branch or surface on which the iguana is lying when he performs an acknowledgment bob. The relaxed dewlap will hang loosely in drapey folds, quite different from the rigidly extended, flared-out dewlap.
With a new iguana, that may be a way of relieving stress: if I don't see you, you can't bother me. In the wild they would do this to another iguana acting aggressively. By shutting it out, it signals that it is not interested in returning the aggression.
With an established iguana who is in a new place or when there are strangers around, keeping the eye nearest you closed and away from you open can signal that the iguana is comfortable with you, knows that nothing harmful is going to come from your direction (that's what you are there for, after all) and so it is keeping a watchful eye on the unknown.
Bobs may be done in a variety of situations, signaling different things. Some examples of male bobbing include acknowledgment of your presence; a warning that it wants to be left alone; a sort of visual equivalent of scent-marking, such as when the iguana enters a room or climbs up to the top of a basking or lounging area. Females will also bob when they are annoyed by the attention of others or to warn others (including you) away from their area. While they are not as territorial as males, they sometimes do not want others around them when they are eating or basking. (See also Head Bobbing...)
When we humans work with babies or our dogs or cats, we often try to quiet them by making a "shhh-h-h-h-h" sound. We have been socialized to know that when we hear this sound, it means to be quiet. When an iguana hears this sound, however, he will most often take it as a threat, a somewhat incompetent click-hiss. Instead of quieting an iguana, especially a new or untamed iguana, it may result in a renewed bout of aggressive or defensive behavior. When I am working to calm a wild iguana, I make a "tsk-tsk-tsk" sound instead. When I want to threaten or intimidate a particularly wild and stubborn iguana to establish my dominance, I will then resort to head-bobs, click-hissing (no namby-pamby shhh-h-h-h-ing for me!) and open-mouth threats.
Some iguanas who are involved in aggressive or dominance encounters will sit, body tensed, on alert, their mouths only slightly agape. Many people, not realizing that the entire posture signals a threat, think their iguana is grinning or smiling. Iguanas, like other reptiles, do not have the facial musculature to smile or grin. A grinning iguana such as described above is one who is likely ready to bite or nip at an even minor provocation - an event that will most certainly not bring a smile to the owner's face!
A Note on Open Mouth
In captivity, however, for some reason their cues seem to be mixed up. Perhaps it is because so often they are being kept on bottom heat, or because the bright white light intensity cues available to them in the wild are missing in captivity. Whatever the cause, the result in a captive iguana is one who sits in a spot that is too hot but from which it will not move - so it opens its mouth to pant in an attempt to cool the blood circulating in its mouth tissues to spread cooler blood through the body. This, of course, is highly ineffective. It is thus up to the iguana keeper to move the iguana out of the heat and begin to gently and gradually cool them down. The best way is by spraying them with water or placing in a tub of lukewarm--not cool and certainly not cold--water.
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