Field study of the social behavior of the black lizard, Ctenosaura pectinata. American Museum novitates ; no. 1493

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New York : American Museum of Natural History
"A colony of 22 lizards (Ctenosaura pectinata) was located on the loose-rock wall of a cemetery near the village of Acapancingo, near Cuernavaca, Morelos, Mexico. This colony was studied during the late winter and spring. Animals were identified by such distinguishing marks as broken or regenerated tails, specific markings of the neck, the degree of blackness of the skin, and by individual behavioral traits. Each tended to remain on or in the vicinity of a particular rock, usually one located slightly higher than others along the wall. These sunning or lookout stones were between 15 and 30 feet apart. Three of the females shared sunning rocks with their mates, while two females occupied separate points along the wall. Among the adult males a hierarchy, which comprised at least eight individuals, was found to exist. The highest ranking male preëmpted the right to trespass upon the footage of any other male that dwelled upon the wall. If he encountered any sign of opposition as he crossed a territorial boundary he merely opened his jaws threateningly and passed on while his lesser rivals crawled down into the crevices until he had passed. The 'tyrant's' nearest neighbors on the wall possessed the same right of trespass but to a very much more limited degree. They never passed over the 'tyrant's' holding, which was located at the highest point of the wall, at the north corner, even though it was closest to the food supply. All members of the colony fed, unmolested by the 'tyrant,' upon bean seedlings in the near-by field and drank from the near-by stream. Each individual actually possessed no more 'territory' than the narrow strip of wall that extended halfway between his lookout rock and that of his neighbors on either side of him. This small footage was defended against encroachment by all except the 'tyrant' himself, and on rare occasions by a male who held a footage on the wall next to that of the 'tyrant.' All lesser males in the hierarchy respected one another's territorial rights and were never observed to trespass. It is believed that this colony type of lizard society evolved from the simple individual territoriality, which is still prevalent in C. pectinata that occur far from tilled soil. The daily 'tour of inspection' that the 'tyrant' makes along the walls of the cemetery represents a vestige of the habit that black iguanas, like most lizards that live in non-agricultural regions, have of patrolling their individual territories, each of which would be greater in area than the entire bean field and cemetery combined. With the advent of agriculture in Mexico many centuries ago, the concentration of succulent food in small fields surrounded by loose stone walls provided ideal ecological conditions for large herbivorous lizards such as those of the genus Ctenosaura. Such an environment may have resulted in adaptive behavioral changes, especially on the part of low-ranking individuals in the group. This is indicated by the fact that, although all eight males in the hierarchy exhibited varying degrees of pugnacity during the period of observation, only male A regularly threatened the others and preëmpted the right of at least temporary trespass on their resting areas. By yielding to male A, the lesser members of the hierarchy gained the unusual security of the rock walls as dwelling places and enjoyed the bountiful food to be found in the gardens. In untilled areas no colonies were observed; instead, individuals were widely dispersed, and no hierarchy was possible. Rivals no doubt fought for a territory, but the defeated animal simply moved on in search of another area"--P. 23-24.
26 p. : ill. ; 24 cm.
Includes bibliographical references (p. 24-26).