Social aggregation by thick-tailed geckos (Nephrurus milii, Gekkonidae): does scat piling play a role?

Communal deposition of faeces into scat piles plays a role in pheromonal communication among group members in many 'social' vertebrates, including the scincid lizard Egernia stokesii. How general is this apparent link between scat piling and sociality? Thick-tailed geckos (Nephrurus milii, Gekkonidae) are large nocturnally active lizards that are widely distributed across southern Australia. They spend the daylight hours inactive inside retreat sites, typically rock crevices or burrows. Unusually among geckos, these animals often form groups of several individuals at these times. Our observations of captive N. milii showed that they also form discrete scat piles. However, habitat-selection experiments suggested that adding scats to a crevice did not modify the lizards' probability of using that crevice. Thus, although Nephrurus milii scat pile (at least in captivity), communal faeces deposits do not appear to serve a social role in this taxon.