Model for vocalization by a bird with distensible vocal cavity and open beak

Area of Science:

• Bioacoustics
• Animal Vocalization
• Avian Acoustics

Background:

• Many bird species produce complex vocalizations for communication.
• Some songbirds, like the Northern cardinal (Cardinalis cardinalis), are known for their nearly pure-tone songs.
• The anatomical structures enabling such vocalizations are not fully understood.

Purpose of the Study:

• To acoustically analyze the vocal system of the Northern cardinal.
• To understand the mechanism by which birds produce nearly pure-tone songs.
• To investigate the role of the oropharyngeal-esophageal cavity in song production.

Main Methods:

• Acoustical analysis of the bird's vocal system.
• Examination of the oropharyngeal-esophageal cavity's resonance.
• Modeling the effect of cavity volume, beak gape, and tongue position on sound radiation.

Main Results:

• The oropharyngeal-esophageal cavity acts as a resonator, venting through the beak.
• This resonance creates a dominant peak in radiation efficiency.
• The frequency of this peak is adjustable via cavity volume, beak gape, and tongue position.

Conclusions:

• Birds adjust the resonant frequency of the oropharyngeal-esophageal cavity to match the syringeal fundamental frequency.
• This mechanism allows for the production of nearly pure-tone songs.
• The study provides a detailed acoustical explanation for this specialized vocal behavior.