Mate choice based on static versus dynamic secondary sexual traits in the dark-eyed junco

Abstract

Some secondary sexual traits (SSTs) such as structural characteristics are semi-permanent or static, while others, such as courtship display, are more labile or dynamic. In this paper we report results from two experiments designed to test the relative attractiveness to female dark-eyed juncos (Junco hyemalis, Passeriformes, Aves) of a relatively static plumage trait, the amount of white in the tail, and a relatively dynamic behavioral trait, courtship intensity. The experiments derived from a study showing that female juncos prefer males that court more vigorously. We asked whether females also base their preferences on plumage traits and how they respond when presented with a choice between attractive traits that are either static (plumage) or dynamic (courtship) in nature. In the first experiment we presented males to females in paired mate-choice trials and found that males enhanced with more white in their tails were more attractive to females than controls with unenhanced tails. Females spent more time with enhanced males and directed more sexual displays toward them. In the second experiment we tested whether females preferred males with enhanced tails (a static SST) or males with enhanced hormone-mediated courtship behavior (a dynamic SST). In this experiment females did not demonstrate a consensus preference for either the static or the dynamic trait. Instead, some females preferred the male whose courtship performance was enhanced with testosterone, while others preferred the male with an enhanced tail. We conclude that both kinds of traits are important in junco mate choice, but that some females apparently weigh static traits more heavily than dynamic ones, while other females use opposite weightings.