The second plumage of a bird that takes more than one year to obtain adult plumage (e.g. eagles). Usually but not always acquired at one year of age and usually worn for a year. It is followed by Basic II, Basic II, etc. .
^Clark, William S.; Brian K. Wheeler (2011). Hawks of North America, 2nd Edition. Boston, MA: Houghton Mifflin Company. p. 12. ISBN0395670675.Cite uses deprecated parameter |coauthors= (help); |access-date= requires |url= (help)
This article is part of Project Glossary, a All Birds project that aims to write comprehensive articles on each term related to animals.