Female Choice of Mates: A General Model for Birds and Its Application to Red-Winged Blackbirds (Agelaius phoeniceus)

Abstract

A model of female choice in birds is developed with special reference to red-winged blackbirds. Characteristics of the male are related to female fitness, and it is argued that these characteristics should influence mate choice only if they (a) have an important effect on female fitness, (b) are variable, and (c) are accurately assessable prior to mating. Using these criteria, it is concluded that female choice in redwings (1) should not be influenced by the female's estimate of the male's future nest defense effort because nest defense seems to have little effect on the severity of predation and parasitism losses; (2) should not be influenced by an estimate of the male's future time investment in feeding the young because this investment is small in redwings, and the female's estimate must be inaccurate; (3) should be influenced by the vulnerability of the territory to predation because predation rates are high, variable from area to area, and predictable; (4) should not be influenced by the vulnerability of the territory to cowbird parasitism because parasitism losses are lower and less predictable than predation losses; and (5) should be influenced by the availability of food to a female on the territory because starvation rates are substantial, marshes are known to be variable in productivity, and productivity should be predictable before mating. Male genetic quality could also influence female choice, but the importance of this factor cannot be evaluated as it is not known how strongly the fitness of offspring is influenced by male genetic quality nor how accurate is the female's estimate of genetic quality. Empirical tests indicate that territory quality influences female choice more than male genetic quality and that male defense effort has little influence.