Conspecific Attraction and Aggregation in Territorial Species

Abstract

For many years, field studies of birds have suggested that territorial individuals may be attracted to one another, forming territorial clusters independent of resource distributions. However, virtually no experiments have studied these phenomena in either the laboratory or the field. The present field study was designed to test whether prospective territory owners preferentially settle near conspecifics and form territorial aggregations when territory quality is held constant. Juvenile Anolis aeneus lizards arriving at juvenile habitats in clearings were given a choice of artificial homesites arranged around a clear-walled enclosure divided into two parts, one of which contained resident A. aeneus juveniles. Juveniles showed a clear preference for the homesites adjacent to the established territorial residents (the "experimental" homesites). In each of eight trials, the first arrivals appeared on the experimental homesites. Juveniles that first appeared on the experimental homesites were more apt to settle in the clearing, and colonists on the experimental side moved around less before choosing a final territory. During the colonization process, juveniles spent more time on the experimental sides of the enclosures; and by the end of the trials, more juveniles had eventually settled on the experimental homesites. Throughout the settlement process, new territory owners tended to cluster around the previous residents within the experimental side of the enclosures. These results indicate that A. aeneus juveniles are attracted to conspecifics while settling a territory and that this process can lead to territorial aggregations that are independent of territory quality.