greyish brown above, paler below. Immature birds independent from their parents have lost most of the mottling (except on the wing coverts) and barring, but their wing stripe and underside are still dull white, shading to brown on the flanks; any white tail feather tips appear at this stage. The northwesternmost populations of major might be confused with Turati's boubou (L. turatii), which has no white wing-band and a buff chin and white belly, while major around the southern edge of the Congo Basin look almost identical to the swamp boubou (L. bicolor), but this is pure white below and its females give a characteristic "ratchet" call in duets. Southeastern birds (mossambicus and especially limpopoensis) resemble the southern boubou (L. ferrugineus) but are black above instead of dark brown and grey – though this may be hard to see at a distance and entirely indistinguishable in the occasionally seen hybrid. When the tropical boubou is sympatric with other Laniarius, they are rarely found in the same habitat. Voice This species is heard more often than seen, but its calls often help to locate it visually. To vocalize they move higher off the ground than during their usual activities, and may perch on an exposed site. They also nod their head and bow their body when calling, making them even conspicuous sometimes. Calls like or give the bird its name; they may be extended into a bubbling and are given loudly and higher-pitched to announce the birds' presence, or lower and softer by foraging groups to maintain contact. Like many bush-shrikes, it has a wide vocal repertoire that includes duets in which two individuals – a male-female pair or two males with adjacent territories – give notes alternately in so rapid a sequence that they sound like one bird. As the voicebox of birds is a syrinx not a larynx, in particular many Passeri can sing in two voices at the same time; tropical boubous that have lost their mate can make the same sequence that a pair would make. Males probably start most duets, and their notes are mostly low-pitched whistles and/or harsh croaks; females' notes are typically higher whistles and/or "harsh tearing or rattling sounds". But although the birds' vocalizations are somewhat harsh, they are still able of a wide range of frequencies and males provide the higher voice in certain duets. Duets usually consist of one exchange, two