Disseration Research: Ecological and Hormonal Bases of Paternal Care in the Chestnut-collared Longspur, Calcarius ornatus

University Of Washington, Seattle WA

Investigators

Abstract

Male birds participate in parental care more than males of any other vertebrate group. Thus, birds represent an extraordinary model to untangle the various factors that affect care of young. When breeding begins, males experience a rise in the hormone testosterone (T) that declines by the time young hatch. This pattern may represent a trade-off between T levels and expression of paternal care: experimentally, high levels of T are associated with reduced paternal care in favor of enhanced sexual behavior. In chestnut-collared longspurs (CCLO), experimentally increased T enhances sexual behavior before eggs hatch, but surprisingly, does not reduce care of nestlings. This study will test the hypothesis that this unusual insensitivity to T during the parental phase occurs because males are critical for nestling survival. By manipulating environmental and hormonal variables, this study will determine (1) if male care is essential, (2) if the environment drives male care, and (3) if elevated T affects nest defense in CCLO. Male care, though generally rare in nature, is prevalent in birds. Whether paternal care is driven by environmental factors or by internal cues, however, is unknown. This study will help to unravel the relative roles of hormones and environmental cues on the expression of paternal care. Determining the role of environmental factors in the apparent trade-off between T and paternal care is particularly important, because it can be applied to additional systems in which paternal care is critical for survival of young.