Can House Finches (Carpodacus mexicanus) use non-visual cues to discriminate the carotenoid content of foods?

Carotenoid pigments are involved in different physiological processes (e. g., immunoenhancement, antioxidant activity) in addition to coloring plumage and integuments. As animals cannot synthesize these pigments de novo, it has been proposed that carotenoids constitute a limiting resource that birds may specifically seek in their food. Confirming this hypothesis, it was recently found that birds can discriminate between carotenoid-enriched diets and control diets, even if both have the same color, suggesting that there may be underlying non-visual (e. g., olfactory, taste) mechanisms for detecting carotenoid presence or enrichment in foods. In this study, we performed two experiments with male House Finches (Carpodacus mexicanus) to test if this species is able to discriminate between (1) carotenoid-enriched and plain sunflower seeds (while controlling for food coloration), and (2) plain seeds scented with β-ionone, which is a carotenoid-degradation product that is common in many fruits and is one of the most powerful flavor-active organic compounds, or a sham odorant. We found that finches did not show significant food preferences in either experiment, indicating that they did not use odor or flavor cues associated with carotenoids to discriminate between foods. However, our results do not rule out the possibilities that other flavors or odors can be used in discrimination or that finches may learn to discriminate flavors and odors over longer periods of time or at other times of year through post-ingestive feedback mechanisms.