Where to do number two: Lizards prefer to defecate on the largest rock in the territory

Many animals use their excrements to communicate with others. In order to increase signal efficacy, animals often behaviourally select for specific defecation sites that maximize the detectability of their faecal deposits, such as the tip of rocks by some lizard species. However, the field conditions in which these observations are made make it difficult to reject alternative explanations of defecation site preference; rock tips may also provide better opportunities for thermoregulation, foraging, or escaping predators, and not solely for increasing the detectability of excrements. In addition, we still know little on whether lizard defecation behaviour varies within-species. In this laboratory study, we take an experimental approach to test defecation site preference of Podarcis melisellensis lizards in a standardized setting, and assess whether preferences differ between sexes, and among populations. Our findings show that in an environment where all stones provide equal thermoregulatory advantage, prey availability, and predator pressure, lizards still select for the largest stone in their territory as preferred defecation site. Moreover, we demonstrate that lizards' defecation preference is a strong conservative behaviour, showing no significant intraspecific variation. Together, these findings corroborate the idea that lizards may defecate on prominent rocky substrates in order to increase (visual) detectability of the deposited faecal pellets.