TÌM LỖI SAI + GTH Birds that feed on flocks commonly retire together into roosts. The reasons for roosting commune are not always obvious, but there are some likely benefit. In winter especially, it is important for birds to keep warmth at night and conserve precious food reserves. One way to do this is to find the sheltered roost. Solitary roosters shelter in dense vegetation and enter a cavity- horned larks dig holes in the ground and ptarmigan burrow into snow banks- but the effect of shelter is magnified by several birds huddling together in the roosts, as wrens, swifts,brown creepers, bluebirds, and anis can. Body contact reduces the surface area expose to the cold air, so the birds keep each other warm. Two kinglets huddling together was found to reduce their heat losses with a quarter and three together saved a third of their heat.

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