Age-related parental care in a long-lived bird: implications for offspring development

In long-lived species, behaviour is expected to vary across the lifespan, first improving with maturation and experience and then declining with senescence, but measurement is rare, particularly during old age. Measuring nest defence intensity in 255 known-age blue-footed boobies ( Sula nebouxii ) of 19 age classes confirmed the inverted-U pattern: intensity of nest defence increased in young males and females until roughly 11–12 years and declined progressively afterwards. We discuss the processes that may generate this distinctive pattern. Regardless of the underlying processes, this study establishes the existence of age-related variation in parental care in a long-lived species. Natural variation in natal conditions has recently been shown to have long-term impacts on development, so this study raises the question whether age-related changes in parental care generate systematic variation in offspring phenotypes. Significance statement In theory, age-related change in parental care can result in differences among offspring produced at different ages. However, parental behaviour has never been measured over the whole age-span of any long-lived species because of the difficulty of sampling very old animals in the field. We measured intensity of nest defence over the age-span and confirmed that blue-footed boobies exhibit an age-related quadratic pattern in this parental behaviour: defence intensity increases in early life and declines progressively afterwards. Our results imply that similar-shaped patterns may exist in other components of parental care, such as feeding and social interaction, potentially affecting the long-term development of offspring.