Phenology and ecology of color in bird-dispersed fruits, or why some fruits are red when they are "green"

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Abstract
Several hypotheses regarding the ecology of color in bird-dispersed fruits in North America are presented and tested. (1) We predicted, but failed to substantiate, an inverse relationship between size and colorfulness of fruiting display. Large fruit crops are more often bicolored than small ones. Red monochrome fruits are relatively common in herbs, but we cannot say if red is more "conspicuous" to birds than blue or black nor if herbs are relatively less conspicuous, when in fruit, than shrubs or trees. (2) Conspicuous displays are most common in plants that fruit at times when avian frugivore abundance is low. This hypothesis is supported strongly by the phenologies of temporally bicolored displays, which are produced commonly in summer before the influx of fall migrants. Data from morphologically bicolored displays are less clear-cut. Temporally bicolored displays may increase fruit dispersal particularly by juvenile birds and (or) decrease conspicuousness to invertebrate predators, as well as increase the level of display attractiveness to whatever dispersal agents are present at the time. (3) Conspicuous displays occur in regions where frugivore abundance is seasonally low. This hypothesis receives some support. A comparison of Illinois (low diversity and numbers of wintering frugivores) with the Carolinas (where both are high) suggested that monochrome displays may be relatively more common, and morphologically bicolored displays less so, in the Carolinas. High frugivore abundance and diversity may relieve competition for dispersors and reduce selection for unusually conspicuous displays.

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