I am broadly interested in the evolution of communication as well as the proximate mechanisms by which animals can produce dynamic signals and overcome interference when discriminating dynamic signals in the natural environment.

Birds often modulate their vocalizations over a wide range of sound frequencies (2-8 kHz). Sound frequencies below and above ~3.5 kHz, however, are expected to encounter different physical forces upon production, propagation, and reception. My research has therefore revolved around the premise that songbirds may often communicate within at least two different sound frequency channels as a way to facilitate communication, where a 'channel' is defined as the proportion of a frequency spectrum that is used for a specific purpose. Furthermore, and if communication can be defined as the formation and use of associations between signals, signalers, locations, and innumerable other events, then one way to facilitate or expedite 'communication' may be to form and use different associations within at least two different sound frequency channels (i.e., sound frequencies below or above ~3.5 kHz).

Eastern towhees (Pipilo erythrophthalmus), for example, use at least one association to estimate how 'loudly' a distant bird has vocalized. They then use a second association, attenuation of amplitude over distance, to discriminate distance. These associations are relatively strong below ~3.5 kHz but are comparatively weak over higher sound frequencies due to several factors, including unpredictable changes in: (1) attenuation over distance, (2) the vocalizing bird's beak gape, (3) orientation, (4) height above the ground, (5) direction, and so forth. Nevertheless, towhees rarely misjudge distance when sound frequencies above ~3.5 kHz in vocalizations are varied in amplitude. They therefore seem to use at least one additional association with distance ('cue') when they hear these higher sound frequencies. Binaural 'cues' that are associated with direction (azimuth & elevation) may further facilitate or expedite the formation/use of countless additional associations since an ability to accurately discriminate direction is expected to reduce acoustic degradation. Interestingly, different binaural cues (ITD and ILD) are thought to function best over these same two sound frequency ranges/channels.

Future studies will continue to focus on the syntactics and pragmatics of dynamic communication systems as well as the mechanisms that can be used to overcome interference from the environment (pragmatic disturbances).