Do a flower’s features help hummingbirds to learn its contents and refill rate?

Colour is a cue that animals can use to categorize rewards and may be particularly important to nectarivores, which forage on flowers that vary in hue. Here, we investigated whether colour facilitated the learning of the properties of artificial flowers in free-living rufous hummingbirds, Selasphorus rufus. Whereas refill rates and sucrose concentrations of flowers were readily learned, we could not detect in the birds’ performance an effect of colour on the learning of either floral property. As these results seem unlikely to have been the result of a ceiling effect or an inability to perceive colour variation, we suggest they are due to overshadowing. This apparently counterintuitive result, where birds do not attend to what appears to be a very prominent cue, is consistent with evidence that hummingbirds pay more attention to space than to colour.