ABSTRACT

Differences between the sexes have long been a source of fascination for people. This is especially true for ornithologists because birds have provided many of the model examples for the evolution of sex differences in body form and behavior. Charles Darwin devoted several chapters to birds in his 'Descent of Man and Selection in Relation to Sex' (Darwin 1871), and considered them to be more important for their diverse secondary sexual characters than any other taxonomic group. Darwin referred to such species as the Peacock (Pavo cristatus) with its elaborate male plumage and long trains used in display, the Brown songlark (Cincloramphus cruralis), where males appear similar in plumage to females but are much larger in size, and the Ruff (Philomachus pugnax), where males are both larger than females and have elaborate breeding plumage (Darwin 1871).