Does large size make daughters of the blue-footed booby more expensive than sons?

Abstract

1. In species where size dimorphism emerges during parental care, individuals of the larger sex are presumably more expensive to produce than individuals of the smaller sex. 2. We evaluated whether female offspring of the blue-looted booby, because of their larger size, require greater parental feeding expenditure than males. 3. A field experiment compared growth rates of sons and daughters when hand-fed the same amount of food, and a descriptive field study compared the parental feeding rates to fledgling sons and daughters. 4. Females maintained greater rates of mass and ulna increase than males when fed the same amount of food. 5. First-hatched chicks had higher probability to be fed than second-hatched chicks. However, male and female fledglings were fed at similar rates by their parents. 6. No evidence that daughters of the blue-footed booby receive a greater feeding expenditure than sons was found. Faster motor development of males in this facultatively siblicidal species might explain why they grow more slowly than females with the same food budget.