Nest Microclimate, Water-Vapor Conductance, and Water Loss in Heron and Tern Eggs

• Published in: The Auk 1983-01, Vol.100 (1), p.76-83
• Main Authors: Vleck, Carol Masters, Vleck, David, Rahn, Hermann, Paganelli, Charles V.
• Format: Article
• Language: English
• Subjects: Animal nesting; Aves; Biological and medical sciences; Bird nesting; Egg masses; Eggs; Embryology: invertebrates and vertebrates. Teratology; Fundamental and applied biological sciences. Psychology; General aspects. Development. Fetal membranes; Humidity; Incubation; Marine; Thermocouples; Water loss; Water pressure; Water vapor
• ISSN: 0004-8038; 1938-4254
• DOI: 10.1093/auk/100.1.76

Rates of water loss$(\dot{M}_{{\rm H}_{2}{\rm O}})$were measured in eggs of seven species of tree-nesting Ciconiiformes and three species of ground-nesting Charadriiformes during natural incubation. Measurements of egg temperature, conductance of the egg shell to water vapor, and nest and ambient humidity allow one to calculate the difference in water-vapor pressure (ΔP) between egg and nest and between nest and ambient air. ΔP between egg and nest was significantly lower in ground-nesting species (23 torr) than in tree-nesting species (31 torr). We suggest that low ΔP in ground-nesting species was due to relatively high humidity (ca. 27 torr) in nests built on the ground compared to the humidity in loose stick nests of tree-nesting species (ca. 14 torr). Water-vapor conductance of eggs from more humid nests is relatively higher than that of eggs from less humid nests (107% and 78% of predicted values, respectively), resulting in similar fractional losses in mass for the whole incubation period in both groups of birds.$\dot{M}_{{\rm H}_{2}{\rm O}}$was not always constant throughout incubation. We suggest that changes in$\dot{M}_{{\rm H}_{2}{\rm O}}$may be due to changes in ambient humidity and/or egg temperature.