Increase In Pore Density Research Articles

Regional Changes in Shell Thickness, Shell Conductance, and Pore Structure during Incubation in Eggs of the Mute Swan

Shell thickness, water vapor conductance, pore density, and pore structure were examined in three regions (blunt pole, equator, sharp pole) of both unincubated and hatched mute swan eggs. There was a trend for shell thickness to increase from the blunt pole to the sharp pole in unincubated eggs. During incubation, shell in the equatorial and sharp pole regions was eroded so that shell thickness in all regions was similar in hatched eggs. Pore density and water-vapor conductance of unincubated eggs were significantly smaller in the equatorial region, compared with that in either the blunt or sharp pole regions, but increased during incubation. Pore structure of unincubated eggs was similar in all three regions. The removal of the mammillary knobs from the equatorial and sharp pole regions during incubation caused the shell to thin but had a negligible effect on pore structure. Therefore, the increase in water-vapor conductance in the equatorial region during incubation was directly related to the increase in pore density that occurred in this region.

Incubation Water Loss by Pied-Billed Grebe Eggs: Adaptation to a Hot, Wet Nest

Eggs of pied-billed grebes (Podilymbus podiceps) are incubated in warm, wet nests built of decaying vegetation 3–7 cm above the waterline. The daily mass loss (Ṁh2o) of 52 grebe eggs in their nests was 157.6 mg · day−1 (±SD 13), resulting in a 16.4% loss of mass during the 23-day incubation period. Eggshell water vapor conductance (Gh2o) was 12.3 mg · day−1 · torr−1 (±SD 1.8), a value 2.7 times greater than predicted for other bird eggs of similar mass and incubation period. The high eggshell conductance is the result of a threefold increase in pore density. The bottom of the unincubated but covered nest cup remained at 31–33 C despite floating in water at 20 C and air temperatures ranging from 10.8 C to 23.6 C (June). Water vapor pressure around the eggs is elevated owing to the warm, wet nest, thus requiring an increase in eggshell conductance if the eggs are to lose sufficient water. Incubating adults leave the nests unattended (but covered) for prolonged periods of time. This behavior may be related to the maintenance of a suitable egg temperature by the warm nest material.