A comparative analysis of passerine mobbing calls

We examined the acoustic structure of mobbing calls of 52 species of passerines representing an array of taxa. Marler suggested that calls given during mobbing have characteristics enhancing locatability that include abrupt onsets and a wide frequency range. Only about one-half of the species we studied produced calls during mobbing that had these characteristics. However, clicks (probably produced by bill snapping) sometimes were given during dives at predators. Vocalizations given during mobbing were quite diverse in acoustic structure. Two trends were noted: phylogenetic patterns; and possible convergence in certain species engaged in interspecific flocking.