Relating to or situated in the apteria, the bare or sparsely feathered areas of a bird's skin.
From apteria (bare feather tracts) + -al (adjective-forming suffix). This ornithological term describes features or characteristics of the featherless regions of bird skin.
When ornithologists map out a bird's apterial regions, they're basically creating a feather-free GPS coordinate system on the bird's body!
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