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 <1C 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., >1C) 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. / Doctor of Philosophy / Animal parents can have large effects on the development of their offspring. In birds, an important way that parents affect their offspring is through incubation, where parents physically warm their eggs to stimulate embryo development. Eggs must be incubated in order to hatch, but recent research has shown that small changes (<1C/2F) in average incubation temperature have major consequences for the quality (e.g., size, ability to thermoregulate) of offspring after they hatch. However, parents must balance how they spend their time and energy between incubation and other important activities (e.g., eating, avoiding predators), and thus incubation behavior and temperature can vary among birds. Understanding which factors affect incubation, and the consequences of altered incubation temperatures for the offspring, will help us to better understand how animals care for their offspring and how environmental changes may influence offspring development. I investigated how human disturbance, environmental temperature, and the number of eggs in the nest influenced parental incubation behavior and egg temperatures, and subsequently how egg temperatures affected offspring behaviors. By studying wood ducks (Aix sponsa) in the wild, I found that parents spent less time incubating after a human disturbance (i.e., capture) than before (Chapter 1), egg temperatures increased as environmental temperatures increased, and egg temperatures decreased as the number of eggs in the nest increased (Chapter 2). Further, in nests with many eggs (>12), some eggs experienced much lower average incubation temperatures (>1C/2F difference) than others in the same nest (Chapter 2). Then, by studying wood duck ducklings in an aviary, I found that ducklings incubated at lower temperatures were less successful at exiting a nest (Chapter 3), exhibited bolder and more exploratory behaviors (Chapter 4), were smaller, and consumed less food (Chapter 5), than those incubated at a higher temperature. Together, my dissertation shows that the number of eggs in a nest, environmental temperatures, and human disturbances can influence parental behaviors, which then affect offspring. This has broad implications for understanding why birds lay the number of eggs that they do, how animal behaviors develop, and how environmental changes (including those caused by humans) can affect wildlife.