For the first time, scientists have detailed evidence that an animal can see color by starlight. People lose color discrimination in such dimness, but hawkmoths aced tests of color recognition at night.
Some older studies suggested that goldfish and a different moth see colors in dim light, but Almut Kelber of Lund University in Sweden and his colleagues focused on the Deilephila elpenor hawkmoth, which collects nectar during the darkest hours of the night in Europe.
The researchers trained moths to associate sugar-water with either yellow or blue artificial flowers. When offered an array of colored and gray choices, moths settled on the color they’d been trained to seek. Even as the researchers dimmed the light from dusk to starlight, moths still picked the right color most of the time, the investigators report in the Oct. 31 Nature.
To see whether the moths had managed their feat just by exquisite sensitivity to shades of darkness and lightness, the researchers offered a wider selection of flowers, including a darker and a lighter version of the target color. The moths rarely investigated flowers in the completely wrong hue–a sign of recognition of the hue itself–but did show interest in the alternative versions of their treat-associated color.
Moths even can compensate for shifts in the color of illumination, the researchers say. Moths trained to select green artificial flowers managed to alight on them even when yellow light made a turquoise decoy appear, at least to a human eye, to be green, as well.
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