‘Sympathetic Song’: the Silent and the Overt Vocal Repertoire, Exemplified with a Dueting Pair of the African Slate‐Coloured Boubou, Laniarius funebris

In many bird species the total song repertoire consists of an overt repertoire normally uttered, and a silent repertoire produced only under special circumstances. A silent repertoire can be inferred from specific vocal responses of an individual to hearing parts of its own silent repertoire uttered by another bird (‘sympathetic song’). The silent repertoire plays a prominent role in dueting birds, in particular those with sex‐specific overt song repertoires, where the overt repertoire of one partner is the silent repertoire of the other. This is here exemplified with a pair of the slate‐coloured boubou L. funebris. Silent repertoires should be taken into consideration when relating the complexity of birds' vocal behaviour to the size or structure of their forebrain vocal control areas.