Feathers are the core feature of birds, responsible for multiple functions such as flight, insulation, courtship, and waterproofing. Their maintenance is one of the most frequent daily behaviors of courtyard birds in the Americas, mainly achieved through combinations such as grooming, oil baths, and sand baths.
1. Precise sorting: Reconstructing feather structure and function
Most courtyard birds have specialized "feather combs" - the fine serrated structure of the beak edge, combined with the keratinized spines on the surface of the tongue, which can finely comb their feathers. When the main sparrow inhabits the bushes in the courtyard, it will hover or dock sideways, and use its beak to comb its feathers and down feathers one by one, focusing on the hook shaped structure between the feather branches. If these hooks are separated by flight or rainwater, it will cause the feathers to become fluffy and lose their streamline. Birds can use their beaks to peck and pull the hooks back together, restoring the density of the feathers. Blue Jay will use the branches in the courtyard as "support points", spread its wings and place them on the branches, and comb the easily knotted feathers under the wings to avoid abnormal air resistance during flight.
For areas such as the head that are difficult to reach with the beak, birds will use their claws for assistance. When the swallow rests on the clothesline in the courtyard, it often lifts one foot and hooks the feathers on its head with the tip of its claw, cooperating with the rotation of its head to complete the combing process. Its movements are flexible like "self massage". This combing behavior can be repeated dozens of times a day, especially after flight or rainfall, the frequency will significantly increase.
2. Oil bath and waterproofing: activate the "natural protective layer" of feathers
The tail fat gland (located below the coccyx) of many courtyard birds in the Americas can secrete oil containing wax and fat, which is their "natural waterproofing agent". When active by the shallow water pool in the courtyard, the flapping wing beetle will first insert its beak into the tail fat gland, peck out the oil, and evenly apply it to its feathers. During the application process, they will pay special attention to the joint between the feather shaft and the feather blade of the flying feather, ensuring that the oil penetrates into the stratum corneum and forms a waterproof film. Observing the main Cardinals in the courtyard after rain, one will find that the water droplets on the surface of their feathers roll off in a spherical shape, which is the result of the oil layer playing a role in preventing their feathers from absorbing water and causing weight gain and body temperature decline.
3. Sand bath and ant bath: "biological therapy" against parasites
Feather lice and mites in the crevices of feathers are common threats to birds, and courtyard birds in the Americas use environmental resources for "biological control". Blue ravens often dig shallow pits in the dry sand of the courtyard, lie prone in them, shake their wings and twist their bodies to let sand enter the gaps between their feathers, then stand and shake their whole body, using the friction of the sand to remove parasites and dirt. This sand bathing behavior is similar to "natural sanding".
Even more intelligent is the "ant bath" behavior, where swallows, main Cardinals, and others actively search for ants active in the courtyard, peck them with their beaks and apply them to feathers, or directly let ants crawl into the crevices of feathers. The formic acid secreted by ants has bactericidal and insecticidal effects, and can effectively kill feather lice eggs. This maintenance method using biochemical substances is the result of long-term co evolution between birds and insects. Some birds also choose citrus leaves in the courtyard, pecking at the sap of the leaves and spreading it on their feathers, using plant ingredients to enhance pest control.
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