Common swift that resemble a crescent or a boomerang. Their call is a loud scream in two different tone pitches, the higher of which issues from the female. They often form 'screaming parties' during summer evenings, when 10–20 swifts will gather in flight around their nesting area, calling out and being answered by nesting swifts. Larger "screaming parties" are formed at higher altitudes, especially late in the breeding season. The purpose of these parties is uncertain, but may include ascending to sleep on the wing, while still breeding adults tend to spend the night in the nest. Swifts may nest in former
Screaming cowbird research has shown the species are not each other's closest relatives. The screaming cowbird frequently parasitizes its main host, the bay-winged cowbird, during the pre-laying period. Screaming cowbirds lay 31% of their eggs before the first bay-winged cowbird egg but most of the eggs laid are ejected, and often within 24 hours. By ejecting parasitic eggs with their feet, bay-winged cowbirds can reduce the parasitic egg load by 75%. Host species can eject an entire clutch and commence egg laying again in the same nest or abandon the nest and start afresh. Chopi blackbirds and brown and yellow marsh birds