Bird Adaptations

How do birds fly?

How do birds sing?

  • Birds have evolved a specialized voice box called a syrinx (SEE-rinks). Unlike in humans where the larynx is located within the trachea (TRAY-keea) close to the mouth, a bird’s syrinx is positioned closer to the lungs where the trachea branches into two bronchi (BRONK-eye).

  • The songbird syrinx (SEE-rinks) is branched—making it possible for some birds in the group to sing two different notes simultaneously. Thanks to independent muscle control on each side of the syrinx, songbirds can vibrate paired tissues called labia (LAY-bee-a) at different rates to make two sounds at once. The technical term for this is biphonation (BYE-fone-ayshun) and in lay terms this feat is usually referred to as two-voiced song.

  • Advance to animate a songbird syrinx (SEE-rinks). This illustration demonstrates how the labia (LAY-bee-a) within the syrinx vibrate independently. In most of the songbirds that have been studied in detail, the left side of the syrinx specializes in lower pitch notes and the right side specializes in higher pitch notes. This specialization allows songbirds to perform vocal gymnastics including seamless sweeps through more pitches than on a piano and two-voiced song.

  • Advance to animate the Wood Thrush syrinx. This short video illustrates the movements of a Wood Thrush syrinx during a two-voiced trill played at quarter speed. While one side of the syrinx repeats a sweeping high-pitched note, the other side repeats a series of mini trills—making this song one of the most beautiful examples of biphonation (BYE-fone-ayshun)

  • Advance to animate a sound pressure wave. Fundamentally, sound is the vibration of air molecules. That’s why there’s no sound in space. Here on earth, air molecules that have been set into motion by a vibrating sound source (like a bird’s syrinx) bump into each other. This creates a cascade of movement that we call a pressure wave because it moves outward in bands of increased air pressure. Because your eardrum is sensitive to tiny differences in pressure, you can detect the airborne vibrations that enter your ear as sound.

  • Advance to step through the labeled waveform view. Since we can’t see sound, it helps to find ways to visualize it. Waveforms, for example, show the peaks and lulls in air pressure over time—the higher the air pressure, the louder the sound. The duration of one wave cycle is called the period.

  • Spectrograms add a helpful dimension to sound visualization by showing changes in pitch and loudness over time. This makes it very easy to see sound patterns at a glance. For a sound that stays at a steady pitch, the spectrogram looks like a horizontal line. Spectrograms can come in many colors, but typically the brighter the color, the louder the sound.

  • Waveforms show the peaks and lulls in air pressure over time—the higher the air pressure, the louder the sound. For simple sounds we can also see differences in pitch on the waveform—with more widely separated peaks indicating a slower moving, longer wavelength, lower pitch sound.

  • Spectrograms can come in many colors, but as on this graph, typically the brighter the color, the louder the sound. Lower-pitch sounds appear lower on the graph and higher-pitch sounds appear above them.

  • Advance to hear and animate the Black-capped Chickadee song. The waveform and spectrogram views are united here to help you understand how they are related and what each view is useful for.

  • Advance to hear and animate elements of the Black-capped Chickadee repertoire. It’s ear-opening to explore the full repertoires of your favorite birds. Beyond the main song, most songbirds also use a variety of calls to communicate. Calls are vocalizations that birds typically use to stay in touch and communicate nearby threats. Songs refer to the vocalization that functions in mate attraction and territory defense. Repertoires can be large—containing hundreds of distinct vocalizations for some species.

  • Advance to hear and animate the practice song and the adult song of a White-throated Sparrow. While some birds hatch knowing their adult songs, true songbirds, or oscines (AH-seenz), need training. They begin by listening to tutors while still in the nest. Following fledging, young birds practice the tunes they memorized as chicks until they’ve mastered the pitch, rhythm, and structure of adult song. The practice songs are referred to as plastic song, or sometimes subsong, while the adult songs are considered crystallized.