a collection of rush-like marsh plants, hence, a group of sea or marsh birds that use it as a nesting place. Also, siege.
Examples : sedge of bitterns; of cranes; of herons—Bk. of St. Albans, 1486.
"Sedge, Sege." Dictionary of Collective Nouns and Group Terms. . Encyclopedia.com. 24 Apr. 2019 <https://www.encyclopedia.com>.