Embryonic mortality as a cost of communal nesting in the delicate skink

Lizards are appropriate organisms to investigate causes and correlates of communal egg laying because their general lack of parental care focuses attention on nest site choice. We field-tested hypotheses associated with nest site choice and communal egg laying in the delicate skink Lampropholis delicata, in south-eastern Australia. Specifically, we predicted that lizards would nest at sites with lower openness and solar radiation than random sites, but within crevices with higher humidity than random crevices. However, we predicted that these environmental factors would not differ between communal and solitary nest sites (based on previous research), but that egg mortality in communal nests would be higher than that in solitary nests due to conspecific interference. Despite being ground dwellers, skinks in this population nested above the ground level in narrow horizontal crevices within vertical faces of sandstone outcrops. At the broadest scale, skinks nested at sites with significantly lower canopy openness and incident (solar) radiation than random sites, while at the smallest scale, skinks nested in crevices with significantly higher relative humidity than potential nest crevices. Humidity averaged 94% in nest sites, and nesting females did not trade-off humidity for temperature, despite an inverse relationship between the two at potential nest sites. Of 60 nests, about half to two-thirds were communal. Communal nest sites did not differ from solitary nest sites with respect to temperature, humidity, rock size, aspect, height of crevice above ground, or crevice dimensions. Eggs from communal nests were three times more likely to desiccate and perish than eggs from solitary nests, a clear cost of communal nesting. Desiccation was caused by eggs being displaced from their original positions within the crevices, possibly by conspecific gravid females.