Differential response to colour tasks on resident and migratory hummingbirds: a field test

Abstract

Foraging performance of different hummingbird species was quantified by experimentally simulating changes in the environment, and we tested the hypothesis that species of migratory hummingbirds are more likely than resident to adjust their behaviour to changes in the environment. Colour discrimination tasks were designed to explore how 120 recently captured hummingbirds perform when the expected rewarding floral colour is not profitable. Hummingbirds were presented with an array consisting of 36 randomly distributed artificial flowers of two contrasting colours, where 18 were empty and either pink, orange or red, and 18 were filled with a sugar solution and were either green, yellow or orange. Although a few individuals failed or gave up visiting the experimental array after few non-rewarding foraging bouts (28%), most hummingbirds foraged continuously (72%). Out of those that foraged continuously, 36% consistently visited non-rewarding flowers and 64% switched to the rewarding colour. On average, migrants visited proportionally more rewarding flowers and were more willing to forage than residents, except the poor performance of one migratory species. Both migratory and resident hummingbirds performed better than chance when foraging on red/orange arrays, but their foraging performance differed on pink/green and orange/yellow arrays. Our results showed that some individuals thrive on risk and novelty while others shrink from the same situation, and that these differences are due to intrinsic differences among individuals in their tendency to switch, or a differential sensitivity to different colour combinations, regardless of their migratory status.