A unique up-slurred call of the willow titParus montanus, renderedpuiorplui, was discovered at a locality in the birch alpine region of central Norway in the summer of 1987 when three neighbouring pairs shared this call. Up to 1996 inclusive an additional number of 19pui-calling individuals were found. Typically, these birds were either offspring of birds already uttering the call, or members of winter flocks in which the dominant adults possessed the call. The call is evidently acquired by learning and serves as an alternative alarm call. It is suggested that rudimentary pui-calls are a normal component in babbling series of young willow tits in general and that the development of these into full calls depends on appropriate tutors. It should be emphasized that the pui-call does not replace another call in the repertoire, but is an extra call adding to the repertoire. It is probably the first time that such a phenomenon has been reported in birds. The expectation that the call would spread in the population has so far proved wrong.