Basically, leks, Food not randomly distributed or at least not defended (super abundant). The species are nomadic and have aggregation points, often traditional. The females raise and feed young; mainly fruit-eating birds. Males display together and the females come in. A few males may inseminate most females--One male White-bearded Manakin managed 73% observed copulations; in Sage Grouse: 75% copulations with 10% of males.
Other birds that use leks include flower sucking: Phaethornis; fruit-eating: manakins (except insectivores), cotingas, and birds-of paradise; seed-eating: grouse; and insect-eating: Buff-breasted Sandpipers and Ruff.
Its been suggested that insects in the Arctic are patchily distributed, so Arctic nesting sandpipers make leks near concentrations of insects.