Melissa Kaplan's
Herp Care Collection
Last updated January 1, 2014

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.


When the dewlap is fully tucked up under the chin, the iguana is signaling submission. It is also a sign that they are being non-aggressive, non-threatening. Baby iguanas are often thought by their owners to not have dewlaps, as the owners never see them for the first several weeks. Once the hatchlings are more comfortable around humans, they relax enough to let them down. Other hatchlings, on the other hand, are quite healthy and feisty, and their little dewlaps are rigidly extended whenever humans look their way.

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.


Eye Closure

One eye:
If the iguana closes just one eye, and that is the one facing you, while keeping the other eye open, that means he is shutting you out.

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.

Both eyes:
Initially, when in the early stages of taming an iguana, closing both eyes may be a complete way of shutting you out. Out of sight, out of mind. As time goes on, however, the eyes closed, in conjunction with a head or body rubbing ("petting") session signals about the same thing you closing your eyes does when you are getting a massage - pure relaxation and enjoyment. If your iguana leans into you when you are petting him, or lifts his head to meet your hand, or gives little air-licks with his tongue every several strokes, you will know that your iguana has finally reached iguana nirvana.


Head-bobbing is a very common behavior. Walk into your iguana's space first thing in the morning, and you are likely to be bobbed. With a highly tamed iguana, it may be a combination of greeting (acknowledging your new presence in the area) and a statement ("This is my territory!"); his not chasing you or raising his body up means that he accepts your presence there. Many people interpret this as being a greeting, an unqualified "Hi!" and will often bob first. When their iguana is less than tame or socialized, this may be interpreted by the iguana as a threat, an act of aggression, and so they get defensive or aggressive in return.

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...)


A low, guttural click-hiss is the only voluntary vocalization an iguana makes. This is generally done with the mouth wide open, tongue arched, and body in full compression with dewlap flared. Hissing signals a sort of "last straw" warning. I have one female who hisses when any other iguana has the temerity to approach her favorite night sleeping spot. Her click-hissing is so loud that I can hear the sound 30 feet away.

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.


Open-Mouth Threat
Iguanas, like many reptiles, will open their mouth wide as a threat. The inside of their mouths is bright pink and, in an excited iguana, it may be engorged with blood making it appear in even more vivid contrast to their surrounding green skin. The tongue will often be displayed, thrust up and out of the open mouth, its bright deep pink forks fully exposed. When in full threat mode, a guttural clicky hissing sound may be heard. The animal viewing such a display is thus hopefully frightened off before actual physical contact is engaged.

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 Behavior...
Iguanas, like many animals, do not sweat. If they get overheated, they will first attempt to move someplace cooler to lower their internal body temperature. At least, in the wild they will do that - retreating out of the sun into the cooler shade, or dropping 10 or 50 feet into the river or stream flowing under their basking branch.

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.


Iguanas who are presenting a threatening stance to a human or another iguana, or presenting for breeding purposes, will often swagger. A stylized form of walking, the body is compressed laterally to make it look taller, and the lizard stands on straightened legs. When walking, the tail may be swished from side to side. The dewlap will be fully extended downwards. When approached, such iguanas will lean over away from you or will circle around you, attempting at all times to present the broadest possible form to you to maintain their threatening look.


This is related to the stylized movements done during a threat or breeding presentation. In this, however, the last half of the tail twitches, much like the tail of a cat who is stalking a bird or ball of yarn. It does seem to signify a condition of mixed motivations. I notice it most in the only iguana I have who tries rigorously to mate with me every year. He does it when in a hunched up position, body in compressed and broadside presentation, but head down, dewlap semi-relaxed in partial submission. This iguana always tries to bite me during the breeding season. He also knows that once he does bite me, it results in very little contact with me for several days after the bite. When he is separated from me, or reduced to minimal contact with me, his coloring goes quite dark, his appetite falters even more than the usual breeding season reduction, and he will often become dehydrated. Behaviorally, he becomes quite subdued, choosing to sleep in cooler areas than when he is acting normally or outside of breeding season. The tail twitching seems to be an indication of his being torn between the two conflicting wants or needs: the want or need to mate (grabbing me with his teeth is the second step in the courtship, after stalking and presenting) conflicting perhaps with the knowledge that what happens to him after the bite isn't much fun. This latter presumes some cognitive or modeling ability, the ability to understand think about future cause and effect, action and reaction, a point still hotly debated by behaviorists.

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