Green Iguana Head Bobbing
©1995 Melissa Kaplan
There are many reasons why green iguanas bob their heads.
Females bob to say:
Contrary to popular belief, females as well as males bob their heads. Males do it more frequently than do females, but bobbing itself cannot be used as a gender determinant. Bobbing can start at any age. As it is typically used in an aggressive way or to assert dominance, and it is generally executed by iguanas who are secure in their surroundings. Females generally bob in a rather jerky, erratic manner - it almost looks as if they are practicing, just learning how to bob. Females bob when irritated (generally at another iguana, less frequently at humans), such as when annoyed by the attentions of a male, or when warning another iguana away from their basking area.
Males have several different bobs. Male bobs are generally fluid, executed smoothly. Bobs are usually straight up and down; some may include side-to-side movement. The shudder-bob is a warning: the head is vibrated quickly in the up-down-sideways mode, the head kept raised upwards after the last movement. This is held for a moment or two, followed by an up-and-down bob. This bob is often addressed to the owner the first time the iguana sees the owner during the day or after a long separation and is delivered from a relaxed, laying down position rather than the raised and laterally compressed body position that typically accompanies the aggressive bobs.
Subordinate iguanas tend to bob more like females than males. Males who have been raised alone and who have not had access to their own reflection also often bob like females. After time, however, in the presence of other males or after several hours in front of a mirror, their bobs are executed in the male mode. Subordinate male iguanas, however, may maintain a low profile in the presence of dominant males by appearing as females, hence the quasi-female bobbing.
Rapid bobbing is usually be a warning or assertion ("This is MY area") to another iguana, a human, or the cat spied sitting on the fence across the yard. Slow bobbing may be a restrained statement of annoyance or warning by a subordinate iguana to a dominant iguana (or human or other creature). Some slow, deliberate bobs may be done when two iguanas encounter each other when they haven't yet had a chance to assess the other. In this case, it is a sort of guarded greeting and assertion ("I'll say 'Hello', but don't get any ideas about messing with me"). If this bob is accompanied by a raised laterally compressed body, there is more warning or defensiveness in the greeting than there is greeting.
Bobs, dewlap extensions, and posture provide the iguanas with a highly varied, often subtle vocabulary with which they communicate. It is up to us to learn to recognize the various combinations and analyze the context in which they are given in be able to begin to understand just what our iguanas are saying.
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