Translations:AY Honors/Australian Birds/Answer Key/57/en
From Pathfinder Wiki
Both sexes have a patch of red skin at the throat that is the gular sac; in male great frigatebirds this is inflated in order to attract a mate. Groups of males sit in bushes and trees and force air into their sac, causing it to inflate over a period of 20 minutes into a startling red balloon. As females fly overhead the males waggle their heads from side to side, shake their wings and call.
