Consequences of avian parental incubation behavior for within-clutch variance in incubation temperature and offspring behavioral phenotypes
Parents can have large effects on their offspring by influencing the early developmental environment. In birds, a major way that parents can influence the early developmental environment is through egg incubation. Not only is incubation necessary for hatching success, but small changes of <1C in average incubation temperature have large effects on post-hatch offspring morphology and physiology. However, incubation is energetically costly and time-consuming for parents, and thus parents must allocate resources between incubation and self-maintenance. This can lead to differences in parental incubation behavior and egg temperatures among and within populations. Understanding which factors influence incubation, and the subsequent effects for offspring, is crucial for understanding parental effects, non-genetic drivers of phenotypic variation, and how environmental changes affect avian populations. I used wood ducks (Aix sponsa) as a study species to investigate how factors (disturbance, clutch size, ambient temperature) that influence parental demands may affect parental incubation behavior, physiology, and egg temperatures, and subsequently how egg temperatures affect offspring behavior and physiology. In a field experiment, I found that nest disturbance (i.e., capture) reduced both parent prolactin concentrations and the amount of time that parents spent incubating (Chapter 1). Further, ambient temperature was positively and clutch size negatively related to egg temperatures. Notably, in large clutches, differences in average incubation temperature among eggs within nests were large enough (i.e., >1C) to lead to different offspring phenotypes within broods (Chapter 2). Then, in a series of experiments in which I controlled incubation temperature, I provided evidence that lower average incubation temperatures lead to a reduced ability of ducklings to exit the nest cavity (Chapter 3), a more proactive behavioral phenotype (Chapter 4), a smaller body size, and a reduced efficiency in food consumption (Chapter 5), compared to those incubated at higher temperatures. Together, my dissertation illustrates how disturbances, clutch size, and ambient temperature can influence an important aspect of avian parental care, which has wide-ranging effects on offspring traits and fitness. This has broad implications for understanding the evolution of clutch size, development of behavior, and the effects of anthropogenic changes on wildlife.