A large dark swift with origami-like angularity in flight profile. Black overall with a slightly paler throat and a bright white rump patch. Long forked tail is prominent in flight and is often opened while the bird is banking. Migrates in enormous flocks, which give sharp trilling calls in flight. The only large “fork-tailed swift” in its range, but compare with Cook's, Blyth's, and Salim Ali's Swifts where ranges overlap.
Exotic species flags differentiate locally introduced species from native species.
Naturalized: Exotic population is self-sustaining, breeding in the wild, persisting for many years, and not maintained through ongoing releases (including vagrants from Naturalized populations). These count in official eBird totals and, where applicable, have been accepted by regional bird records committee(s).
Provisional: Either: 1) member of exotic population that is breeding in the wild, self-propagating, and has persisted for multiple years, but not yet Naturalized; 2) rarity of uncertain provenance, with natural vagrancy or captive provenance both considered plausible. When applicable, eBird generally defers to bird records committees for records formally considered to be of "uncertain provenance". Provisional species count in official eBird totals.
Escapee: Exotic species known or suspected to be escaped or released, including those that have bred but don't yet fulfill the criteria for Provisional. Escapee exotics do not count in official eBird totals.