2023 Author: Bryan Walter | [email protected]. Last modified: 2023-05-21 22:24
Biologists have found that plumage color affects the success of barn owls in hunting, says Nature Ecology & Evolution. Birds with red plumage on moonlit nights brought less prey to the nest than birds with white plumage. The point turned out to be the amount of light reflected from the plumage. More moonlight is reflected from the white plumage and this more blinds the voles (the main prey of the barn owls), so that they are much easier for birds to catch.
Barn owls (Tyto alba) live on all continents except Antarctica. These birds of prey prey on small mammals, reptiles, amphibians and sometimes insects. The barn owls found in most of Europe mainly prey on voles (Microtus arvalis), and less often on shrews. The bird slowly hovers above the ground, hovering over the places where the victim may be. She either eats the prey, or hides it in case of lack of food. European barn owls hatch chicks in March-June. The female incubates the clutch for 29-34 days, and the male feeds her. Parents carry food to chicks in turn. Young barn owls begin to fly at the age of 50-55 days.
The color of the plumage of barn owls can vary from white to auburn. But whether he helps the birds to adapt to their surroundings was not clear. The research results turned out to be contradictory, according to some, the color of the plumage does not affect anything, according to others, it helps predators to hunt.
Evolutionary biologists, led by Alexandre Roulin of the University of Lausanne, have suggested that moonlight will influence the success of barn owls of different colors. On moonlit nights, birds with red plumage will be less visible to voles and will be able to catch more prey. The plumage of white barn owls, on the contrary, will better reflect light and attract the attention of rodents that will run away from them.
The authors tested the hypothesis during a study of barn owls in western Switzerland, which has been going on since 1991. Scientists installed 360 nest boxes on an area of 1,700 square kilometers and, during the breeding season, checked the masonry every 2-3 days. The authors tracked the movements of birds using GPS trackers. The scientists tracked the success of their hunt using infrared cameras installed at 131 nests during the breeding seasons of 1997, 2001, 2005, 2006 and 2016.
The authors' hypothesis was not confirmed: barn owls with a red color hunted most successfully on moonless nights, and when the moon was full, they hunted the least number of rodents (P <0.001). But the moon did not affect the hunting of white birds, every night they killed about the same amount of food.
To test how rodents spot and react to predators of different colors, the researchers conducted behavioral tests. They caught 45 voles and, after adaptation, planted them in small enclosures in a dark room. The full moon in the experiments was simulated by two halogen lamps, and instead of attacking live barn owls, scientists used stuffed birds with a white or red color and with spread wings. Each rodent was shown stuffed birds of different colors at full moon and new moon.
It turned out that the barn owls in the moonlight had a paralyzing effect on the voles. In 83 percent of cases, rodents, seeing an owl, froze on the spot. But the time of daze varied greatly depending on the color of the bird and the presence or absence of the moon. On average, the rodents froze for 9.5 seconds. If they were shown stuffed owls on the new moon, the voles remained motionless for approximately the same time and their colors did not affect their behavior. If voles were shown a stuffed snowy owl under a full moon, they froze 5.2 seconds longer than when they saw a red bird (P = 0.039). And at the sight of a barn owl, the rodents remained motionless during the full moon for 9.6 seconds longer than during the new moon (P = 0.003).
The researchers suggested that the vole was blinded by the light reflected from the bird's feathers. To confirm the hypothesis, they smeared the plumage of the stuffed animal with one of the white owl wax, which reduces the reflection of light from the feathers. At the sight of this stuffed animal, even on a full moon, the rodents remained motionless almost twice less (13.6 seconds versus 26.4, P = 0.018) than when they were shown an owl, whose feathers completely reflected light. On the new moon, voles reacted in the same way to stuffed white birds with plumage and plumage smeared with fat.
Earlier studies have shown that bright light elicits negative responses in rodents (rats and mice) and is an aversive stimulus. Therefore, the authors conclude, voles are likely to react more strongly to brighter light, which is reflected from the white plumage of barn owls. This is confirmed by the experiment with a stuffed animal with greased feathers, to which the rodents began to react weaker.
Barn owls are helped to hunt not only by the color of the plumage, but also by silent flight, as well as hearing acuity, which does not decrease with age. As it turned out, even in a very elderly, 23-year-old individual, hearing deteriorated slightly.