Katherine E. Brooks’s research while affiliated with University of Nebraska–Lincoln and other places

Versatility in song production of birds has drawn considerable attention since its description by Hartshorne (1956), who suggested that birds vary their vocal output to avoid habituation in listeners, especially if singing is extensive. The best-known route to song versatility involves creating permutations and combinations of song elements learned from neighbors or relatives, combined with improvisations (Nowicki et al. 1999). Birds may learn whole songs or individual song elements, which then may be arranged in novel ways. Versatility might be achieved in other ways besides acquiring numerous song types. For example, individuals could shift the tempo of their songs by altering internote or intersong intervals. Alternatively, birds might sing the same pattern of notes but shift their frequency range. Black-capped Chickadees (Poecile atricapilla) shift the frequency of their whistled songs, which has been suggested to function as a repertoire-enlarging strategy (Horn et al. 1992). Without changing the order of song elements, shifts in tempo or frequency might change the perception of the song sufficiently to prevent habituation. Here, we describe songs of three Nightingale Wrens (Microcerculus philomela), which are residents of tropical lowland forests from southern Mexico to central Costa Rica (AOU 1998). The song of this species has a peculiar quality that has struck some observers as being ‘‘random’’ because it is difficult to discern a clearly recurring pattern (Howell and Webb 1995). This distinctive song has been the primary justification for splitting M. philomela from M. marginatus, the Scaly-breasted Wren (Slud 1958; Stiles 1983, 1984).