Relationships between nest humidity and nest types in living archosaurs

Abstract

Nest humidity (Pnest) is important for archosaur incubation because it has a direct effect on the water vapour conductance () of the eggs. Estimates of are commonly used to infer nest type in extinct archosaurs, although it is unknown whether a relationship exists between nest type and nest humidity or between nest type and . In this study, the nests of 54 living archosaur species (i.e. birds and crocodilians) were classified into three generalised nest types, including covered, non-covered cup and non-covered scrape nests, based on their nest architectures. Pnest and ambient humidity of the nesting habitat (Pa) of these species were compared among these three nest types. Statistical analyses show that Pnest is significantly higher in covered nests than in the non-covered nests, including both cup and scrape types, indicating that the covered nests are significantly more humid than the non-covered nests. Although Pa is lower than Pnest in all species, Pa is not significantly different among the three nest types. These results suggest that although Pa has a fundamental affect on Pnest (i.e. Pnest ≥ Pa), the nest humidity is affected by the architecture of the nesting materials, that is the covered nests are shown to retain more humidity than the non-covered nests.