The mysterious 'purple world' of birds

Starling birds.

While humans can only see 3 types of light: red, green and blue, the bird has the ability to be sensitive to ultraviolet rays. In other words, for birds, we are colorblind.

Philipp Heeb of the University of Lausanne (Switzerland) learned about starling and painting, how to handle them when bringing food back to the flocks in the nest. Since they can't meet them all in one go, which children do they choose to feed first? Many studies have shown that mother birds see chicks from their movements or chirps. But Philipp Heeb found another signal that had never been known before: The distribution of food varies according to the intensity of ultraviolet reflection on the chicks' body.

Since the 1970s, ornithologists have known that most birds can sense ultraviolet rays, like many insects, spiders, fish, reptiles and even some mammals (rodents). ). The bird's retina has a fundamental difference: While there are only three types of cones sensitive to red, green and blue light, humans have one more type of cell sensitive to ultraviolet rays. Violet. People do not see a world like them.

In the past, there was very little work on the subject, but for 10 years, experts on bird behavior have had the means to study ultraviolet vision by analyzing the intensity of light radiation thanks to spectrometer. And the continuous results surprise people.

Since 1996, Andrew Bennett and Innes Cuthill at Bristol University (UK) have demonstrated the ability to see ultraviolet spectra that are related to the selection of partners of some birds. When attaching ultraviolet reflective strips to the terns, they found that females liked them more than normal males.

Recently, many studies have demonstrated that some birds detect prey by trace of ultraviolet reflection. So people discover visual information that was previously unexpected, and they explain behaviors that can sometimes translate into other species. In the past year, Dutch scientists have discovered an interesting thing: The male stripper is more attracted by the male with the most reflective UV rays. The male is also more attracted to the enemy, and if they survive, it is because of his physical health. Their descendants are more likely to be like that and reproduce more easily.

Philipp Heeb cares about the relationship between parents and children of birds. He observed the starlings kicking their children: " I see that the chicks and the skin of the chicks reflect the ultraviolet rays. So I think that can play a role in the parents ' recognition ." He and his colleagues began to compare the weight of "normal" chicks with ultraviolet-reflecting chicks. The results were clear: The young starlings were coated with a gel that prevents ultraviolet rays from gaining less weight than birds without gel. In other words, the most "purple" chicks will receive more food from their parents.

The team thinks they may be easily recognized by their parents in the dark nest. They also observed an association between ultraviolet reflectivity and the resistance of the chicks. Thus, this spectrum of light is a major criterion for the survival of young birds, a distinction of vision that we absolutely do not recognize.

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