Nutritional Values of Wild Fruits and Consumption by Migrant Frugivorous Birds

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Abstract
To learn some of the bases for consumption of temperate fleshy fruits by birds, we examined nutritional and morphological traits of temperate fleshy fruits and made laboratory observations on consumption of individual fruit species using 18 fruit species and 11 migrant frugivorous bird species in Illinois. The only seasonal trends in fruit traits were interspecific increases in absolute quantity of potassium and protein per fruit. Fruit energy content did not differ among species having bicolored vs. monochrome or small vs. large fruit displays. The fruit mass consumed was correlated best with dry pulp mass per fruit, providing significant positive correlations in 6 of 11 frugivorous species. Large fruit size relative to bill size did not appear to affect fruit consumption over the range of fruit sizes and bird species used. Because retained energy was correlated with mass consumed, the fruit pulp mass consumed was in most cases a good index of the energy obtained. Some significant differences occurred in digestive efficiency of a bird species eating different fruit species, and among different bird species eating a single fruit species, but no trends were apparent. Regurgitated seeds generally spent less time in a bird than did defecated seeds, facilitating more rapid disposal of seed ballast. Smaller birds defecated only small seeds and regurgitated some small seeds as wells as large ones, whereas larger birds defecated all smaller seeds may larger ones. Consequently, resultant seed shadows may depend upon both bird and seed size.