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
Abnormal behaviour of birds in captivity cages demonstrated that most birds showing this social deprivation had significant behavioural disturbances, such as aggressive behaviour, feather picking, self-mutilation, restlessness, screaming, apathetic behavior, and stereotypies. Cannibalism often occurs in large animal husbandry systems, which are usually impoverished environments with a lack of opportunities. In addition, studies of caged canaries have revealed two common stereotypies. These include spot picking, where birds repeatedly touch a particular spot in the environment with the tip of their beak, and route tracing, a pacing behaviour associated with physical restrictions in movement imposed by the cage. The absence of song learning in zebra finches has