Food Choices by Northwestern Crows: Experiments with Captive, Free-Ranging and Hand-Raised Birds

Abstract

Captive adult Northwestern Crows (Corvus caurinus), foraging individually, were selective of native Alaskan fruits. Most individuals had color preferences, commonly preferring red, blue, or green over yellow. They often favored high-lipid artificial fruits over low-lipid, but only sometimes favored artificial fruits with high levels of corn syrup or sucrose over those with low sugar levels. However, decreased accessibility of the favored fruits generally eliminated the preference for high lipid or high sugar, although accessibility did not alter preferences in parallel experiments with domestic cherries. Artificial fruits with high seed loads were not avoided. In all of the above experiments, individual variation was conspicuous. Crows showed no evidence of learning foliar cues for fruit selection. Hand-raised crows did not prefer the color of the food upon which they were raised. They exhibited extensive individual variation in preferences for color, lipid and sugar content. Free-ranging crows often foraged in groups, lacked the experience of the captive crows with the visual cues available to identify nutrient levels in the experimental fruits, and commonly did not make the same choices collectively as the captive crows. We interpret the extensive variation among individuals, the flexibility of choice, and the difficulty of assessing nutrient levels in conspecific natural fruits as evidence that selection by Northwestern Crows on the fruit traits examined is probably weak and variable.