Tertiary (feather)One of the inner flight feathers of a bird's wing, although not as important in flying as the primary or secondary feathers. The tertiaries (also called 'tertials') are few in number and are embedded in the skin of a bird's 'upper arm'. They are really the innermost secondaries. In a few cases the name 'tertiaries' may be applied to other feather groups, for example, where they are conspicuously long, the scapular feathers.
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From Peter Weaver's Birdwatcher's Dictionary
Copyright © 1981 by Peter Weaver