Incubation conditions are more important in determining early thermoregulatory ability than posthatch resource conditions in a precocial bird.

Recent research in birds suggests that investing in incubation is one mechanism by which parents can enhance the phenotype of their offspring. Posthatch environmental conditions can also shape an individual's phenotype, and it is thus possible for pre- and posthatch conditions to have interactive effects on an individual's phenotype. In this study, we examined the individual and interactive effects of prehatch incubation temperature and posthatch food availability on growth, food consumption, and thermoregulatory ability in wood duck (Aix sponsa) ducklings. Eggs were incubated at one of three temperatures (35.0°, 35.9°, or 37.0°C), and then ducklings were reared on an either ad lib. or time-restricted diet for 12 d after hatching. We found that food availability influenced duckling growth, with the slowest growth occurring in ducklings fed the restricted diet. Incubation temperature also interacted with food conditions to influence duckling growth: ducklings fed ad lib. from the lowest incubation temperature grew slower than ducklings fed ad lib. from the higher incubation temperatures. Most importantly, we found that the improvement in a duckling's ability to maintain body temperature in the face of a thermal challenge was influenced by embryonic incubation temperature but not feeding conditions. Ducklings from the highest incubation temperature experienced the greatest improvement in thermoregulatory performance with age. Our findings suggest that the prehatch environment is more important than posthatch resource conditions in determining some physiological functions and underscores the important role that incubation temperature plays in determining offspring phenotype in birds.