Fruit color choices of captive Silvereyes (Zosterops lateralis)

Fleshy fruits occur in many colors in nature, but red and black predominate. One popular hypothesis to explain the adaptive significance of fruit coloration is that it attracts frugivorous birds that disperse seeds. We presented Silvereyes (Zosterops lateralis), important fruit consumers in southern Australia, with choices in the aviary between both artificial fruits (made from gelatin) and actual fruits (Rhagodia parabolica) of three different colors (red, yellow and white). Silvereyes exhibited a strong overall preference for red among both artificial and real fruits. Although individual birds varied in their color preferences for artificial fruits, all preferred the red fruits of R. parabolica. The consumption rate of real fruits was much greater than that of artificial fruits, which was probably attributable to differences in the characteristics of the two fruit types. Exposure of Silvereyes to a maintenance diet of a particular color for 12 days also failed to alter their collective preference for red fruits. Further, responses to artificial infructescences offering color choices either between or within infructescences showed that Silvereyes preferred red fruits regardless of the spatial format of presentation. The overall fruit color preferences of Silvereyes were based on selection of hue rather than brightness, but within the same hue, some individuals exhibited preferences for particular brightness levels. These results are consistent with the hypothesis that fruit color is related to avian frugivory and suggest that birds can act as strong selective agents on fruit color.