noun
- A featherless area of skin on a bird's body between the feather tracts (pterylae).
Usage: ornithology; technical
Examples
- The apterium on the bird's wing is visible only when the feathers are parted.
- Ornithologists study the apterium to understand feather distribution patterns.
- The apterium appears as bare skin between the pterylae of waterfowl.
- Each species has a characteristic pattern of apteria and pterylae.