Social Dominance in Winter Flocks of Cassin's Finch

Female Cassin's Finches were determined socially dominant over older and yearling males in flocks during 2 winters. Few females disappeared either winter in contrast to males. With number of females limiting for breeding effort, the dominance of females in winter is interpreted as a behavioral modification to maximize reproductive effort. This species' trait and the need to semiannually colonize a new and often unpredictable environment are correlates of an r-strategy. Displays in agonistic encounters are considered homologous to other fringillids. Reasons for the observed disparities in sex ratio or hormonal factors influencing female dominance are not known.