Winter aggregation and its relationship to social status in the tree lizard, Urosaurus ornatus

Winter aggregations have been shown to occur in wild and laboratory populations of some species of lizards. The tree lizard, U. ornatus, was observed in experimental conspecific aggregations during the winter season. It was postulated that these aggregations occur because of limited over-wintering areas, and/or limited access to areas better suited for thermoregulation. The social system of U. ornatus has been well studied. These studies, however, have been restricted to the spring/summer activity season and shed little light on any social interactions that may occur during the over-wintering period. This study showed that in semi-natural enclosures where suitable over-wintering areas were not limited, U. ornatus formed aggregate groups. It was shown that this species preferentially forms winter aggregations in south-facing crevices as opposed to north-facing ones. Neither summertime social status nor sex of individual lizards had a bearing on their location within a given aggregation.