Factors Influencing Microbial Growth and Viability of Wood Duck Eggs

Abstract

Egg viability in birds declines with increasing length of incubation delay and may be influenced by microbial infection and exposure of eggs to temperatures above physiological zero (>24°C). Reuse of nests is common in cavity-nesting species and may lead to increased microbial levels within the nest. Onset of incubation during egg laying may help to maintain viability of first-laid eggs. We manipulated incubation delay of Wood Duck (Aix sponsa) eggs and tested the effects of incubation delay and ambient temperature, as well as the effects of nest reuse and onset of night incubation, on microbial growth and egg viability. Hatching success declined slowly with increasing length of incubation delay, but was not affected by increasing exposure to temperatures >24°C or microbial growth. We found increased levels of heterotrophic bacteria in uncleaned nests, and gram-negative bacteria decreased following onset of night incubation. We suggest early onset of incubation in precocial birds may be more important in reducing incubation period and predation risk than in maintaining viability of first-laid eggs, and that relatively low levels of bacterial infection of eggs at our temperate study site, together with increased antimicrobial properties of Wood Duck eggs and incubation by females before clutches were complete contributed to the negligible effect that bacteria had on egg viability.