Referring to the paler and more translucent inner primaries such as on gulls or raptors [1].
References[]
^Mullarney, Killian; Lars Svensson, Dan Zetterström and Peter J. Grant (1999). Birds of Europe. Princeton University Press. ISBN0691050538.Cite uses deprecated parameter |coauthor= (help)
This article is part of Project Glossary, an All Birds project that aims to write comprehensive articles on each term related to animals.