Song type variants and aggressive context

We asked whether switching among song type variants functions as a graded s ignal of aggression in song sparrows (Melospiza melodia). Song type variant s are different versions of a given song type and are defined by much small er acoustic differences than those defining separate song types. The princi pal evidence that switching between song types functions as an aggressive s ignal, in song sparrows and other species, is that song type switching freq uencies increase during aggressive contexts, for example during simulated t erritorial intrusions,We tested whether variant switching frequencies chang e in the same way, using playback of conspecific song to simulate intrusion s. Male song sparrows showed a significant increase in variant switching fr equencies during intrusion relative to before intrusion. After intrusions, variant switching frequencies returned to pre-intrusion levels. These resul ts are consistent with the hypothesis that variant switching is a graded ag gressive signal, but other inter interpretations are possible, for example, that variant switching is a signal of submission or represents simple prod uction error.