Beak gape dynamics during song in the zebra finch

Abstract

Bird song is a complex communication behavior that requires the coordination of several motor systems. Sound is produced in the syrinx and then modified by the upper vocal tract, but the specific nature and dynamics of this modification are not well understood. To determine the contribution of beak movements to sound modification, we studied the beak gape patterns in zebra finches (Taeniopygia guttata). Subsyringeal air sac pressure and song were recorded together with changes in beak gape, which were monitored with a magneto-sensitive transducer. Beak gape was positively correlated with fundamental frequency, peak frequency, and subsyringeal air sac pressure in all but one bird. For harmonic stacks, peak frequency increased with increasing beak gape, and the relationship between fundamental frequency and beak gape was no longer significant. Experimentally holding the beak open or closed had acoustic consequences consistent with the model in which beak movements change upper vocal tract length and, thus, the filter properties. Beak gape was positively correlated with sound amplitude in all but two birds. The relationship between beak aperture and amplitude may, however, be indirect because air sac pressure is correlated with amplitude and beak gape. The beak is opened quickly and to its widest aperture immediately prior to the onset of sound and at rapid transitions in sound, suggesting that beak movements may affect vibratory behavior of the labia.

Vocal tract filtering and sound radiation in a songbird

“…For example, spectral changes in the songs of several species that were reported by Nowicki (1987) and Hoese et al (2000) appear to occur primarily above ~3.5·kHz. Similarly, spectral changes reported by Goller et al (2004) in zebra finches, Taeniopygia guttata, occur primarily over relatively high sound frequencies. Suthers and Goller (1997) also demonstrated that harmonics of fundamentals below ~3.5·kHz tend to be suppressed when northern cardinals, Cardinalis cardinalis, sing songs with relatively small beak gapes.…”

“…1B; e.g. Goller et al, 2004;Nowicki, 1987;Podos et al, 2004;Suthers and Goller, 1997;Westneat et al, 1993).…”

Vocal tract articulation revisited: the case of the monk parakeet

“…However, most of the different call types are structurally rather similar to those we recorded and only differ in duration and repetition rate (Martella and Bucher, 1990), which makes it unlikely that the calls are produced by different articulatory patterns. Beak gape has been found to correlate with frequency changes in many bird species (Hausberger, 1991;Westneat et al, 1993;Hoese et al, 2000;Podos et al, 2004;Goller et al, 2004). In the current study we detected beak displacement in vocalizing monk parakeets of up to 6.7mm although we could not establish a quantitative relationship with frequency patterns for several reasons.…”

Songbirds tune their vocal tract to the fundamental frequency of their song

“…Various investigators (e.g., refs. [3][4][5][6] have shown that birdsong is often accompanied by frequency-dependent beak movements in which high fundamental frequencies are associated with a wide beak opening, or gape, compared to that at low fundamentals. The fact that experimentally fixing the gape of a singing bird at a large value increases the relative level of the second harmonic when f 0 is low (refs.…”