Water loss during incubation in red bishop (Euplectes orix) eggs

Abstract

The red bishop (Euplectes orix) is a small passerine, breeding in woven, enclosed nests. Incubated eggs lost water at a rate (16,6 mg day^-1) similar to that predicted by the egg weight and incubation period (18,5 mg day^-1). Deserted eggs lost water at a much lower rate (3,1 mg day^-1). The daily variation in water loss was much greater than has been previously reported. Much of this variation is correlated with changes in atmospheric humidity but heavy rainfall, wetting the nest, may also be important. Incubated eggs showed less daily variation in weight loss (co-efficient of variation 41%) than deserted eggs (co-efficient of variation 165%). The estimated nest humidity of deserted eggs (12,6 torr) was close to the mean ambient humidity (13,4 torr). The microclimate of incubated eggs was calculated to have a higher humidity (16 torr) than ambient and this would require nest ventilation of 1,18 lh^-1 to maintain water loss from the eggs.