Bird Families

Gray-green Spotted Pigeon / Ptilinopus purpuratus

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Island life changes living things. Ask the dwarf Asian elephant in Borneo or the tree plantain growing in the Canary Islands. In island isolation, not only the size, but also the color changes - remember the bright birds of paradise of New Guinea and the Hawaiian flower girls. However, these two groups are rather an exception to the general rule for birds. French biologists have undertaken an extensive study of 116 species of island birds and their 116 closest continental relatives from 13 orders and 66 families to make sure that birds on the islands lose their brightness for the most part.

The pink-capped spotted pigeon (Ptilinopus regina) lives in Australia, and its cousin the gray-green spotted pigeon (Ptilinopus purpuratus) lives in Tahiti. Which one is brighter? Photo: Geoff Whalan, RyanStudiesBirds.

Not that this is a big scientific revelation. In several earlier works, insular faintness of birds is noted, but their conclusions are based on a small number of taxa and islands studied, in addition, the assessment of the brightness of plumage in them is subjectively human, and sometimes taken from textbooks or illustrations. The French acted like an adult: British and American museums personally went out, measuring the color of the effigies of males and females with a spectrometer. Then they ran the data through a bird vision simulator to understand how birds themselves see the same plumage, which have four types of photoreceptors - in contrast to trichromatic humans. The number of "color spots" - monochromatic plumage areas, the variety of which is associated with the complexity of visual signaling, was also counted.

So it turned out that, on average, island birds have less bright plumage, with less saturated colors and fewer color spots, both males and females. Scientists emphasize that this is not true for all pairs of species, but for most. And there are explanations for this scenario. First, on the islands, birds most often do not have to share space with related species, and therefore there is no need to declare their identity in any special way. Secondly, in small island populations, genetic diversity is reduced, and it makes no sense for males to signal any special advantages of their genes with bright plumage, and females do not need to be picky. The result is relatively weak selection pressure ... and less flamboyant postcards.

Text: Victor Kovylin. Based on materials: Discover
Research Article: Ecology Letters (Doutrelant et al., 2016)

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