Traits related to fitness are often pleiotropically linked or otherwise constrained in their expression. Organisms therefore trade between fitness components such as number and viability of their offspring. The physiological mechanisms mediating such trade-offs, however, have been poorly...

Life-history theory posits trade-offs between fitness components. Reproduction negatively affects physiology and immune system functioning, and the effect of this form of stress may be mediated by glucocorticosteroids. We manipulated brood size of barn swallows (Hirundo rustica) to study the...

Mothers can influence the phenotype of their offspring by adjusting the quality of their eggs in relation to sex and reproductive value of the progeny. Maternal androgens in the eggs of vertebrates may mediate such adaptive early maternal effects. However, the evolution of early maternal effects...

Avian eggs are rich in carotenoids, which derive from maternal diet where they may be available in limiting amounts. Egg carotenoids may accomplish major roles in antioxidant protection or modulate physiological functions and growth, interfering with offspring redox status, potentially in a...

Secondary sexual characters have been hypothesized to reveal the ability of males to resist debilitating parasites. Although such reliable signaling of parasite resistance may be maintained by parasite--host coevolution, maternal effects potentially provide a previously neglected factor that...

Altricial nestlings compete with their nest mates for resources delivered by parents. Parents may allocate food to nestlings based on reproductive value of offspring. To test the hypothesis that mouth coloration acts as a signal of nestling condition in the barn swallow Hirundo rustica, we...

Structural coloration has been hypothesized to play a role in sexual selection, and we tested whether this was the case in a field study of the barn swallow Hirundo rustica. The dorsal iridescent plumage of barn swallows has a strong reflectance in the ultraviolet (UV) region, with adult males...

Avian brood parasites have evolved striking begging ability that often allows them to prevail over the host progeny in competition for parental resources. Host young are therefore selected by brood parasites to evolve behavioral strategies that reduce the cost of parasitism. We tested the...

Altricial offspring of birds solicit food provisioning by complex begging displays, implying acoustic and visual signals. Different components of begging behavior may function as reliable signals of offspring state and thus reproductive value, on which parents base optimal parental decisions...