Iguanas use a range of head bobs, dewlap movement and positioning, torso compression, gait and other movements to communicate. Figuring out what your iguana is saying to you or someone else can make the difference in how you respond to an encounter…and it’s fascinating to be able to understand what another species is saying.
First, a recap of basic behaviours. Behaviours can be roughly grouped into the following categories:
This is typically exhibited when the lizard feels threatened by a predator. In the wild, this may be snakes, caiman, and various birds and mammals. In captivity, until the iguana feels comfortable in its new home, defensive behaviours are exhibited towards humans, cats, dogs and large objects of unknown intent (garbage trucks, school buses, a previously accepted human wearing a hat or aposematic colors, etc.)
Defensive behaviors include dewlap flares, raising up on all four legs and laterally compressing the torso, dorsal crest rigidity, side presentation, and tail whipping. If the perceived threat doesn’t back off, open mouth gaping and click-hissing may be used as the iguana backs away or tries to circle around the threat.
Territorial defence, Attempted Acquisition/Expansion
Iguanas, especially males, are highly territorial. In the wild, the more dominant males carve out territories into which they will not allow other males. Males will allow females to pass through or spend time in their territory. This probably has probably proven to enhance that males breeding success: let the ladies hang out to bask and eat, and they’ll likely be back during the week or so that they are receptive to mating.
Young males and those not yet strong or tough enough to displace an established male from his territory hang out on the fringes of the area. Some of these males are called pseudofemales: not only do they not yet have the secondary sex characteristics associated with the well-developed dominant males of the same age (larger jowls, “brain bumps”, adult coloring and markings, breeding season colors), their pheromones mimic that of females so that dominant male will ignore them or not pursue too heavily when they come too close.
Behaviors associated with territorial defence or attempting to oust an established male in order to take over a new or additional territory include dewlap flares, raising up on all four legs and laterally compressing the torso, dorsal crest rigidity, side presentation, and tail lashing. When on the ground, locomotion will be by crab-walking – moving forward and back sideways, as they maintain their side presentation towards their target.
By now you’ve figured out that Territorial Defense/Acquisition and Personal Defense behaviors look quite a bit alike. Fortunately, iguanas are smart enough to tell the difference between when they should use one or the other – or when they are seeing another iguana doing one or the other. Since humans are at least as smart as iguanas, they, too, will be able to figure out if their iguana is defending itself or has decided to claim your side of the bed as its preferred sleeping place.
Social Status – Challenging, Defending, and Signaling Submission
It will come as no surprise that the behaviors identified with Challenging and Defending social status look a lot like Personal Defense and Territorial Defense/Acquisition. There is one difference, however: Challenger and Defender will often meet head on, snout to snout. Their heads will be lowered while their bodies often remain hunched up and laterally compressed, their dorsal crest rigid and tail base lifted off the ground. They will face each other, possibly crab walking while pivoting on the point between their noses, as each tries to get the other to back off.
When one of the iguanas gets the upper nose, so to speak, and is able to approach the other iguana who is presented sideways towards him, the iguana will butt his nose up against the sideways iguana, butting against the ribs and working up to the shoulders and neck. During this time, the sideways iguana is generally trying to get turned around to go nose to nose again, or get to the other one’s side, or, deciding that those who run live to fight another day, get the hell out of there. If no such openings present themselves, the iguana who has realized he doesn’t have a chance has one more option: acknowledge the other iguana’s dominant status by submitting.
Submission posture in iguanas is very much like that in dogs. The torso and tail are pressed flat against the ground, as is the head and neck. The flattened iguana will stay there, trying not to move away, while the dominant iguana noses him, possibly biting the skin of the neck or nuchal crest and chewing on or shaking it. The dominant iguana may even climb on the submissive one while retaining hold of the skin of the neck, looking very much like the mating position of a male on a female. Once the dominant iguana feels his point has been made, he will walk off, or he will detach himself (if he has been biting) and step back, allowing the submissive one to slouch-walk away.
Warning Head Bob
Here is a nice example of warning head bobs: dewlap is down but somewhat relaxed (note how it flops a bit with the head movement, rather than being rigidly extended), body in a somewhat relaxed posture, with legs not completely straight and little lateral compression.
Multi-Purpose Head Bob
Under certain conditions (such as here, Vanquishing The Evil Competitor), this head bob is the equivalent of “Who de man” or, to be more species-appropriate, “Who de big lizurd?” Note the up-and-down with a few side sways common to this type of bob, which can also be used at other times, such as when the iguana keeper walks into the room and is greeted by an iguana who is feeling particularly full of himself. It may also be used to express annoyance towards someone, iguana, human or other animal. Note that females will bob like this, too, towards annoying males as well as humans when they feel the situation warrants it.
This is an example of a somewhat relaxed circle walk. Spike is walking in a circle around (we see towards the end of the clip) the LuvDoll. Note the more relaxed position of the limbs and dewlap. He even stops to taste the floor.
Circling Crab Walk
Here both forward and sideways movement is being used in order to get farther away and circle around the object being warned off or checked out.
Note the forward locomotion with the tail lashing, lateral compression, and flared dewlap. This may be used when a threat from some outside agency (human, dog, another ig) is perceived. It is essentially “big lizard” in motion.
Here are wonderful examples of the leaning iguanas will do when the perceived threat is above them. You can see Spike lean way over to the right as he moves around trying to keep the sideways presentation towards the perceived threat. As a side note, some iguanas will lean into your hand when you are petting them, often leaning so far over and so blissed out by the attention that if you remove your hand, the iguanas will fall right over.
Used when exploring a new environment, or an old one which has had some new scents laid down, such as when strangers (human, iguana, or other animals) visit. Note the positioning of the legs: they are bent in the normal walking mode rather than straightened and stiff as in ritualized modes. Note also the tongue touching the floor, used to transfer sent more directly to the vomeronasal organ.
Here the walk starts out like a Ritualized Walk but with less tail lashing. The object being approached is in sight, and the iguana is figuring out the best way to approach it. You can see where he turns and heads directly for the object, in this case cameraman Steve holding the LuvDoll (his version of the LuvSock).
Here is an interesting combination walk that illustrates how tonguing the floor (or another iguana) is not always a benign activity associated with smelling. A male will challenge another male by tonguing the other male’s neck; it is a sort of insult, perhaps comparable to how a human may objectify another human as a way of depersonalizing the other person. In this walk example, Spike has his eye on someone (Steve): he bobs, tongues the floor, and proceeds to walk around towards Steve, speeding up as if to attack, then going into a sideways presentation with the increased lateral compression and straightening of the legs.
The Direct Approach Walk
Spike takes a more direct approach to LuvDoll after circling just enough so that he has a straight shot for the neck. He bobs a bit of the Multi-Purpose Bob, and then heads for the neck. We can’t see exactly what he’s doing, but based on head and neck movement, it appears he is butting or tonguing the LuvDoll. Done to a male iguana, this is definitely an aggressive action. Done to a female, it can be mildly aggressive or checking to see if she’s amenable to being courted.
Note how Spike has hold of the LuvDoll to try to hold it in place while he looks for the right place to bite, working up and around the torso a bit to bite on the dorsal crest. This behavior is quite common both in breeding season when the male works up to the female’s neck, and males biting other males. It is much harder to get one’s mouth around the side of the torso of a comparably sized competitor, so they go for the neck or anywhere along the dorsal crest.
Here we have a great example of the circling walk that ends in a bite to the haunch of the target. As with The Bite I, this may be directed to a female or to a male. In this particular case, since the LuvDoll isn’t moving, a sign of receptivity (or, at least, of “I’m thinking about it…”) in females, and Spike goes for the haunch rather than the neck, it appears he is treating the LuvDoll as a male competitor.
Here Spike is biting the LuvDoll. When one male attacks another, the iguana being bitten tries to get away while the biter tries to hang on and wrestle the other iguana into submission. This is different than mating in that in mating, a receptive female remains rather still, or walks slowly, during intromission. True, the LuvDoll is moving on the uncarpeted floor, but Spike is rather more vigorous in his leg movements than he would be during intromission.
Here is another example of why a torso bite isn’t particularly effective on a similarly-sized iguana. Spike bites but doesn’t get much despite the give in the terrycloth LuvDoll. He apparently doesn’t think much of the taste, either, as he works it through his mouth. This video has a very good picture of the tightened muscles underlying the nuchal and dorsal ridge – note the ridge extending up from the neck and back, which act to increase the height of the spikes, making the iguana look taller and more threatening.
Just Hanging Around
Spike is walking in the backyard, a place he’s walked before, so there is not a great deal of investigative ground licking. You see some exploration, but it’s mostly just moseying along…
Here’s Spike checking out the grass and, oh look! A tasty piece of shed to eat!
The majority of tamed iguanas enjoy being petted, but they don’t always agree on where their favorite place is: some prefer heads and necks, others necks and shoulders, and some, like Spike, likes the area under his chin and throat getting all the attention. While most iguanas are up for being petted at just about any time the human has a few moments to do so, there are times when they aren’t up for it, or otherwise signal when they have had enough. This appears to be what Spike is doing in the second video, by pushing Steve’s hand away with his right foreleg.