The influence of age, body mass, and environmental variability on individual variation in reproductive behaviors of female redhead ducks

Abstract

Variation in life history traits leads to variation in fitness among individuals. The objective of this research was to examine the influence of female age, body mass, and environmental variability on individual variation in incubation patterns, reproductive strategy choice, and brood ecology of female redheads (Aythya americana). Redhead incubation constancy was the lowest reported among duck species. I proposed that incubation patterns are unusual due to prior parasitic behaviors, which result in a poor body condition. Constancy was higher for older hens, at higher ambient temperatures, and for lighter females at the end of incubation. End of incubation body mass may obscure this finding since mass loss relationships are unknown, but I proposed that heavier females at the beginning of season maintain higher constancy. A dynamic state variable model was constructed to predict variation in strategy choice by age, body mass, food availability, and host availability. Model predictions were used to examine theoccurrence of reproductive strategies on a population level. Strategy choice was influenced by body mass, age, and host availability, whereas food availability fine-tuned decision making. Predictions indicate that parasitism is exhibited in most situations, while nesting only is relatively rare. A captive study was conducted to examine mass loss relationships and verify the predicted relationship between body mass and strategy choice. Body mass was significantly different at the beginning but not at the end of incubation. Thus, end of incubation body mass obscured the relationship between constancy and mass. The predicted relationship between body mass and reproductive strategy choice was supported in captivity. Finally, the influence of age and body mass on brood survival, habitat use, and brood movements was examined. Body mass influenced brood survival and brood movements among habitats, while age influenced only habitat use.