Mate Choice by Multiple Criteria in a Monogamous Species

Abstract

Although many studies emphasize a single criterion of choice, organisms are likely to select mates by several criteria. Males and females may utilize different criteria, reflecting their sex roles. This paper examines the preferences of fetal pigeons for mates varying in several traits: plumage color, plumage pattern, age and previous reproductive experience, and dominance status. Pigeons make discriminations regarding all of these traits. Moreover, results support predictions previously presented (Burley 1977b): Females are more selective in choosing mates and vary less in their tendency to be selective than do males; within each sex higher quality (i.e., more preferred) phenotypes display greater selectivity. No trait was tested for which males are more selective than females. Results are consistent with contemporary sexual selection theory. To facilitate comparisons, an index of selectivity (S) is presented. This index takes into account consistency of a chooser category's preference for a particular phenotype and its tendency to select nest boxes. The index reveals that not all traits appear to be equally important in mate choice. On criteria judged to be more important all individuals are relatively discriminating; on others, few phenotypic classes are selective. Comparing more and less important criteria, selectivity drops faster for low-quality individuals of each sex; this suggests that not only are high-quality individuals more discriminating with regard to each trait, but also that superior individuals select by more criteria than do inferior individuals. Selectivity must be viewed as a relative rather than absolute quantity. For pigeons, selectivity appears to vary seasonally and probably changes with increased isolation from heterosexual courtship. Moreover, at this time, no numerical value can be assigned to the "quality" of various phenotypes. As a result, the primary value of the quantitative index remains qualitative: It facilitates comparisons within and between the sexes and permits evaluation of the relative importance of various traits in mate choice.