Secondary sexual characters may have evolved in part to signal resistance to parasites. Avian song has been hypothesized to be involved in this process, but the role of parasites in modulating acoustic communication systems in birds remains largely unknown, owing to lack of experiments. We...

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...

Bird song has been hypothesized to evolve, partly, to signal health status of males, and song features should therefore correlate with parasite load. Immune function, parasitism, and secondary sexual characters can, however, differ between age classes, and any apparent relationship between song...

Many hypotheses have been proposed to explain why female birds start to incubate before clutch completion (IBCC). Some of those suggest that the resulting hatching asynchrony (HA) is adaptive because it increases the size hierarchy among offspring and in turn reduces nestling competition and...

Stress may have consequences for the evolution of condition-dependent sexual traits. For example, stress may be related to sexual traits through immune function, and sexual traits can reflect how individuals bear the costs of stress-mediated immunosuppression. However, male traits may be...

Yolk androgen deposition is a widely investigated maternal effect in birds, but its adaptive value is at present unclear. The offspring fitness correlates of natural yolk androgen levels are virtually unknown, whereas manipulations largely focused on testosterone and neglected other androgens....

In a polygynous mating system, females settling with already mated males often experience low mating success due to the reduced parental contribution of the male. However, there are numerous factors that may still make it advantageous for some females to choose this mating status. Facultative...