Incubation temperature influences locomotor performance in young wood ducks (Aix sponsa)

Incubation temperature is an important maternal effect in birds that can influence numerous offspring traits. For example, ducklings from eggs incubated at lower temperatures have lower growth rates, protein content, and are in poorer body condition than ducklings from eggs incubated at higher temperatures. Based on these observations, we predicted that incubation temperature would indirectly influence performance through its direct effects on body size. Wood duck (Aix sponsa) eggs were incubated at three ecologically relevant temperatures (35, 35.9, 37°C). After hatching, all ducklings were housed under identical conditions and were subjected to aquatic and terrestrial racing trials at 15 and 20 days posthatch (dph). Contrary to our prediction, incubation temperature did not influence most duckling body size parameters at 15 or 20 dph. However, incubation temperature did have a strong influence on locomotor performance independent of body size and body condition. Ducklings hatched from eggs incubated at the lowest temperature had significantly reduced maximum aquatic swim velocity than ducklings from higher temperatures. Maximum terrestrial sprint velocity followed a similar pattern, but did not differ statistically among incubation treatments. To our knowledge, this is the first study to demonstrate that slight changes in incubation temperature can directly affect locomotor performance in avian offspring and thus provide a significant source of phenotypic variation in natural wood duck populations.