Neural correlates of bird song involve the volume of particular song nuclei in the brain that govern song development, production, and perception. Intra- and interspecific variation in the volume of these song nuclei are associated with overall brain size, suggesting that the integration of...

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...

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...

In some passerines, parents allocate more food to offspring with the brightest red gapes, but the function of parental decisions based on offspring gape coloration is unknown. We hypothesize that gape coloration is part of a communication system where nestlings reveal their condition to...

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...

Birds often lose feathers during predation attempts, and this ability has evolved as a means of escape. Because predators are more likely to grab feathers on the rump and the back than on the ventral side of an escaping bird, we predicted that the former feathers would have evolved to be...

Bird song is usually considered to have evolved in the context of sexual selection. Because extrapair paternity is a major component of sexual selection, mating advantages at the social level for males that produce songs of high quality may be transformed into higher success in extrapair...

We estimated the statistical power of the first and last statistical test presented in 697 papers from 10 behavioral journals. First tests had significantly greater statistical power and reported more significant results (smaller p values) than did last tests. This trend was consistent across...

Among bird species in which males contribute to nest building, sexual selection has favored larger nests. I investigated determinants of nest size in the barn swallow Hirundo rustica and how nest size changed during the period 1977--2003, when tail length (a male secondary sexual character)...

Condition-dependent expression of secondary sexual characters and measures of immune function in a cohort of similarly aged male blue peafowl Pavo cristatus was used to test whether different sexual signals provide information about different aspects of phenotypic quality. A measure of...