Evolving relationships between animals and plants are often patchy in their occurrence in both space and time. If the relationship is mutualistic, selection should act to maximize the probability of interaction between the participants. In the mutualistic interactions between temperate fleshy fruits and birds, the timing of fruit ripening affects the probability of seed dispersal by birds. Rapid removal of ripe fruits is important for some summer and fall fruiting species because of a high probability of fruit destruction by invertebrates (Thompson and Willson, 1978). Production of fruits at a time when birds do not remove them may be selectively disadvantageous in that destruction by invertebrates precludes successful dispersal. Therefore, bird-dispersed plants in temperate regions are commonly supposed to ripen their fruits in fall, after the avian breeding season during which birds often concentrate on insects (Morton, 1973) and during the fall migration (Snow, 1971; Stebbins, 1971). This paper examines the selective pressures acting on the seasonal timing of mutualistic interactions between temperate fleshy fruits and birds. Specifically, it (1) compares the removal rates of mid-latitude fruits before, during and after fall bird migrations, (2) analyzes seasonal variation in the ripening patterns of plants in the context of frugivore availability, and (3) provides a theoretical framework for future work on the phenology of temperate fruit/bird interactions. A fleshy