or three calls in total. But up to seven exchanges have been recorded. A duet may be repeated up to 75 times, and in experiments where the birds were confronted with taped vocalizations, they could be enticed to up to 200 duets. A dozen or more duet types exist, and some seem to confer specific information, forming a Morse code-like sort of language. Examples of typical duet sequences include and . During territorial contests of subspecies major, a wide range of duet types is sung, in particular 1–3 and 9–11. Playback of duet types 1, 2, 9 and perhaps 6 elicits duets of the same type, as well as of others; types 2 and 6 are typically also answered with types 9 and 11, and type 9 with type 3 and perhaps 11. Duet type 5 of major consists of one to several dozen (typically about 3) short call notes given simultaneously by territorial pairs. Its loud male calls are at about 1.4 kHz, 0.4 seconds and downslurred, while the female calls increase in frequency between 900–1,000 hertz, are less than half as long, and begin about halfway through the males' calls. After a pair has prevailed in a song contest with an intruder, the birds quieten down for some time and ascertain that the contestant has called it quits; then, they usually move to a prominent perch, the male at the very top with his mate below, and sing duet type 5. This vocalization might be considered a sort of "victory chant", conferring information about the events to neighboring pairs. Northern birds typically give resonant or whistles, variously short or drawn-out. Among southern birds, grating and calls, snoring croaks and rattling are more common. Other harsh calls, like a metallic or are given by the male in aggression and courtship; eastern birds may also give call at the end of a courtship display. Alarm calls are a variety of chattering outbursts; before roosting, birds often make a series of calls, and they also give a call when the parents change to brood the eggs or young. During social interactions, the wings are often forcefully shaken, producing a ripping mechanical sound. This species may duet with the slate-colored boubou (L. funebris). Trios are common, especially young birds learning to sing tend to join in when a pair duets. Nestlings that want to be fed give high repeated chirps, as usual