Definitions for "Crissum"
That part of a bird, or the feathers, surrounding the cloacal opening; the under tail coverts.
also called undertail coverts, are the contour feathers behind the vent and covering the bases of the Retrices.
The crissum are feathers in a triangular area on the undersurface of a bird between its vent and the base of its tail feathers. One can tell whether a bird is adult or juvenile by looking at the crissum: Adult females tend to have conspicuous dusky edging to most of the feathers on the crissum; whereas juvenile females tend to have nearly pure white crissum.