Female Pied Flycatchers fail to respond to variations in nest humidity

Abstract

We examined the possibility that a cavity-nesting passerine, the Pied Flycatcher ( Ficedula hypoleuca), can modify the permeability of its eggs to water vapor facultatively in response to variations in nest humidity ( P N). We found no significant relationship between the water-vapor conductance ( G E) of flycatcher eggs and P N. In addition, incubating female flycatchers failed to change their patterns of incubation when we modified P N experimentally. These data, coupled with large variations that occur in the G E of the eggs within individual clutches, suggest that Pied Flycatchers do not alter the structure of their eggs as they lay them and may not be aware of differences in P N. It is more likely that G E is determined genetically and has been established by natural selection for eggs with high degrees of hatchability.