Avian eggs: barriers to the exchange of heat and mass

Area of Science:

• Avian reproductive biology
• Thermoregulation
• Heat and mass transfer

Background:

• Bird eggs exchange heat and mass with their environment.
• Boundary layers around eggs influence these exchanges.
• Understanding these processes is crucial for avian incubation success.

Purpose of the Study:

• To quantify boundary-layer conductance to heat exchange for bird eggs.
• To determine how boundary-layer conductance scales with egg mass.
• To compare the roles of the boundary layer in heat versus mass transfer.

Main Methods:

• Measured boundary-layer conductance to heat exchange for various bird eggs.
• Used Nusselt-Reynolds relationship for spheres and thermal properties of air for calculations.
• Modeled heat and mass transfer scaling with egg mass.

Main Results:

• Boundary-layer conductance to heat exchange scales with egg mass to the 0.53 power.
• Boundary-layer conductance to heat and mass transfer scales similarly with egg mass.
• The boundary layer is the primary barrier to heat exchange, but not mass flux.

Conclusions:

• Bird egg incubation involves a significant boundary-layer resistance to heat.
• Incubating birds can modify heat flux gradients and conductance.
• Birds have limited ability to alter mass flux gradients between eggs and the environment.