Aggregation in Bibron's Gecko, Chondrodactylus bibronii

Aggregation behaviour in a rock-dwelling gecko Chondrodactylus bibronii was investigated. In a laboratory setup, individuals were provided with an excess of shelters to determine whether limited availability of optimal shelters may be the cause of this species' aggregation behaviour in the wild. Chondrodactylus bibronii grouped significantly more than predicted by the urn model of random occupation, hinting at mutual conspecific attraction as a possible mechanism for the observed aggregating behaviour. A slight temperature gradient in our laboratory setup, however, precludes a firmer conclusion. In addition to the laboratory study, a field-survey was conducted to investigate the incidence, size and composition of groups. The proportion of solitary C. bibronii individuals (39%) in our sample was more than double that found in the group-living lizard, Cordylus cataphractus where the mechanism for aggregation behaviour is known to be mutual conspecific attraction. Similar to small groups of C. cataphractus, the C. bibronii groups in our sample never contained more than one adult mate. Like in C. cataphractus, solitary males were also found to be significantly smaller in body size than group-living ones. Unlike in C. calaphractus, there was no statistical difference in the proportions of solitary males and solitary females in our sample. It thus remains unclear whether aggregation in C. bibronii is induced by limited availability of optimal shelters or whether it is the result of mutual conspecific attraction. Our data provide support for both mechanisms.