Wild hummingbirds discriminate nonspectral colors (original) (raw)

2020, Proceedings of the National Academy of Sciences

Many animals have the potential to discriminate nonspectral colors. For humans, purple is the clearest example of a nonspectral color. It is perceived when two color cone types in the retina (blue and red) with nonadjacent spectral sensitivity curves are predominantly stimulated. Purple is considered nonspectral because no monochromatic light (such as from a rainbow) can evoke this simultaneous stimulation. Except in primates and bees, few behavioral experiments have directly examined nonspectral color discrimination, and little is known about nonspectral color perception in animals with more than three types of color photoreceptors. Birds have four color cone types (compared to three in humans) and might perceive additional nonspectral colors such as UV+red and UV+green. Can birds discriminate nonspectral colors, and are these colors behaviorally and ecologically relevant? Here, using comprehensive behavioral experiments, we show that wild hummingbirds can discriminate a variety of...

Spectral sensitivities of photoreceptors and their role in colour discrimination in the green-backed firecrown hummingbird ( Sephanoides sephaniodes

Journal of Comparative Physiology A-neuroethology Sensory Neural and Behavioral Physiology, 2008

We studied the photopic spectral sensitivity in the green-backed firecrown, Sephanoides sephaniodes, a South American hummingbird, and its possible ecological relationship with preferred flowers and body colouration. Avian colour vision is in general tetrachromatic with at least four types of cones, which vary in sensitivity from the near ultraviolet (UV) to the red wavelength range. Hummingbirds represent an important family of birds, yet little is known about their eye sensitivity, especially about the role of photoreceptors and their oil droplet complements. The photopic electroretinogram shows a main sensitivity peak at 560 nm and a secondary peak in the UV, and may be explained by the presence of four single cones (λ max at ~370, 440, 508 and 560 nm), and a double cone (λ max at 560 nm) screened by oil droplets. The flowers preferred by the firecrown are those in which the red–green wavelength region predominates and have higher contrast than other flowers. The crown plumage of males is highly iridescent in the red wavelength range (peak at 650 nm) and UV; when plotted in a high-dimensional tetrachromatic space, it falls in a “red + UV” purple hue line, suggesting a potential significant communication signal for sexual differentiation.

Relative colour cues improve colour constancy in birds

The Journal of Experimental Biology, 2017

A ripe strawberry looks red to our eyes in sunlight and in the green light of a forest, although the spectrum of light reflected from its surface differs dramatically. This is caused by two effects, colour constancy, and our ability to learn relative colour cues: the ripe strawberry remains relatively "redder" than an unripe green strawberry. While colour constancy - the ability to recognize colours in shifted illumination - has been studied in many animals, the use of relative colour cues is investigated more rarely. In a previous study on chickens, we measured how large illumination shifts their colour constancy mechanisms tolerate without reliable relative colour cues. Here, we show that chickens remain colour-constant over larger illumination shifts, if they can use such relative colour cues. As relative colour cues are readily available in natural environments, we suggest that their use contributes strongly to colour constancy performance in nature.

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