Development of Parent-Offspring Interactions

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9306988 Clark In many species of birds and some mammals, parents raise families of young that differ in age, size and sex. When providing food, parents face the problem of how to distribute it among these young. The young of many birds must signal their hunger by begging behavior. A number of very general theories predict how parents should allocate care and how much effort offspring should make to get it. However, there are few studies of exactly how parents might discriminate between individual young to provide for their particular needs and, further, how younger or smaller siblings compete successfully for care. This study will address these questions with field experiments and observations of red-winged blackbirds, a species that has not only age differences within broods but also sex differences in growth rate. The behavioral differences among siblings due to age and sex will be documented in controlled tests of those motor and visual abilities that would allow them to beg effectively from their parents. These tests will allow Dr. Clark to identify critical periods when the differences in competitive abilities between older and younger siblings are greatest. Field experiments will be used to test parents' ability to recognize and give appropriate care to young of different developmental stages. Both developmental testing and experiments will be used to assess whether or not younger siblings can accelerate the development of some abilities such as vision, a flexibility that might help them compete with their older siblings. This study will contribute to our understanding of parent-offspring interactions in several ways. It will be the first to investigate exactly how a helpless nestling bird's size, age, and sex compared to its siblings affect its interactions with its parents. It will thus help to provide a needed empirical base for theoretical explanations of parent and offspring behavior in vertebrates. Secondly, this study may extend our animal mo dels for family-level interactions, a current research focus in human psychology. The central question addressed in this area is how the presence and identity of siblings alters the family environment and changes the interactions between a parent and each developing offspring. Altricial bird broods, unlike same-age litters of altricial mammals, make excellent analogs of the age-staggered human family, albeit on a much shorter time scale. Finally, the study of visual development utilizes an unusual camera technique used for studying myopia in human infants. As a first study of visual accommodation in passerine (perching) birds, the data on nestling blackbirds will add to our understanding of the development of visual accommodation and its function in vertebrates, including humans.