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 one pair will lay only 2 eggs in the host nest. Up to 12 female screaming cowbirds can parasitize the same bay-wing nest. Screaming cowbird adults frequently pierce the eggs of their hosts as well as previously laid parasite eggs. One study found 22.5% of bay-winged cowbird eggs were punctured by the screaming cowbird. Screaming cowbirds can distinguish between their eggs and those of other species and laboratory trials have shown that screaming cowbirds will puncture shining cowbird ("Molothrus bonariensis") eggs more frequently than their own. The purposes of egg puncture behavior are not clearly understood but may provide the