nd Territorial Control
By Dr. Kristin Berry
BLM Zoologist
The Social Structure; Tyrants, Territories, and Dominance Hierarchies
THE social structure of a chuckwalla population is complex and is exciting to students of animal behavior. The complex structure may be related to the longevity of the species.
he social structure and organization of the population are controlled chiefly by the dominant males, which are called tyrants. A chuckwalla tyrant is a large, aggressive adult male with a full length or regenerated tail. The tyrant possesses both a harem and a territory and controls the behavior of subordinate males in his territory. If a tyrant loses more than an inch or two of his tail, he loses his social status and is no longer a tyrant.
yrants possess, defend and actively patrol a territory during spring. The territory size ranges from 0.7 to 3.9 acres. Territories are smaller than the home ranges of the tyrants and are superimposed over numerous home ranges of subordinate males and females. Each territory contains portions of home ranges of several other lizards.
Tyrants maintain territories and dominance over subordinate males by three techniques: threat displays (intimidation), chasing and fighting. The intimidation or threat display is accomplished from a prominent basking site well in view of the subordinate. Threat is particularly effective in ridding the territory of immature or juvenile males. The mere presence of the tyrant 20 to 30 yards away can cause a smaller male to back down the far side of a rock.
If numerous threat displays fail to remove the subordinate from view, the tyrant will chase him. During the chase, the tyrant often snaps at the subordinate and sometimes tries to leap onto and ride his back. Chases vary in length from one to 75 yards.
Actual physical combat occurs infrequently. Most fights involve tyrants defending territorial boundaries. Fights may last as long as 50 minutes, with the lizards rolling over and over on the ground. Most subordinate males have home ranges that include the territories of two or more tyrants, and thus are dominated by more than one tyrant. A tyrant generally does not allow any male to remain within his territory (if he sees him). So the subordinates must constantly travel back and forth between territories, trying to avoid the big males.
There is still another interesting feature in the social system - dominance hierarchies. A dominance hierarchy is a system of social relationships where the outcome of aggressive encounters is predictable. Some individuals are consistently dominated by others.
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Courtship
With few exceptions, tyrants do all the courting. They court or are courted by females of all ages. Tyrants are polygamous and have harems of up to five females. However, these large males are not promiscuous; they court the same females on a daily basis throughout the season, forming a pair bond.
Courtship is elaborate and unusual. There are two distinct types of courtship, which are related size and age