Plural of pterium; the areas of a bird's skin that are bare of feathers or have only sparse feathers.
From Greek a- (without) + pterion (feather or wing). In ornithology, apteria refers to the featherless tracts on a bird's body, contrasting with pterylae (feathered areas).
Birds are basically feather-covered Swiss cheese—their bodies are strategically bare in specific patches called apteria, which reduces weight for flight!
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