Hummingbirds are known for their ability to hover in midair and fly backwards, as well as for their iridescent plumage. But some species of hummingbirds also make distinct chirping, squeaking, or whistling sounds with their wings as they fly. This phenomenon has intrigued ornithologists and bird enthusiasts for many years.
Wing Feather Adaptations
The wing feathers of hummingbirds have evolved over time to allow for not only powered, sustained flight, but also the ability to produce sounds. The 10 primary wing feathers are narrow, stiff, and have sharp edges that can catch the air. The covert feathers that overlay the base of the primaries are loose and flexible. It’s this combination of stiff and flexible feathers rubbing together that causes the chirping or whistling noise that is noticeable when some species take off in flight.
Which Species Produce Sounds?
While all hummingbirds are capable of making some incidental noise while flying, certain species have wings that are specially adapted to create more conspicuous chirps, squeaks, or whistles:
- Anna’s hummingbird – Produces loud squeaks during courtship or territorial displays
- Costa’s hummingbird – Makes sharp squeaks and whistles during breeding displays
- Allen’s hummingbird – Males produce loud chirps made by tail feathers during courtship dives
- Streamertail hummingbird – Makes distinctive chirps and whistles in flight
Within these species, it is often only the males that vocalize with their wings, as part of courtship and territorial displays during breeding season. The differences in wing sounds enables identification of species in areas where ranges overlap.
Two Main Hypotheses
Ornithologists have proposed two main hypotheses for why some hummingbirds evolved the ability to produce distinct sounds with their wings:
1. Courtship Displays
Making a chirping or whistling sound with the wings allows male hummingbirds to more effectively display for females during courtship. The sounds highlight their aerial agility in flight and can help attract the attention of females.
2. Territorial Behavior
Loud wing chirps and squeaks may also play a role in male territorial behavior. The sounds signal a male’s dominance and aggression towards competing males that may intrude on a feeding territory. This helps establish boundaries and resolve conflicts without physical contact.
The Mechanics of Wing Sounds
The exact aerodynamic mechanisms that allow hummingbirds to produce chirps and whistles with their wings have been closely studied:
Chirps
- Formed by airflow between stiff primary feathers and loose covert feathers
- Pitch can be modulated by changing wing angle
- Louder when produced during a rapid dive or ascent
Whistles
- Formed by airflow over the primary feathers during directional changes
- Airy, whistling quality created by air vibration
- Changing wing position and angle alters the tone
High speed video and audio has revealed the precision involved in modulating wing position to control the sounds. The muscles that allow such dexterity have evolved specifically for this physical display in species that utilize wing sounds.
The Selective Advantage of Sound
The ability to produce chirps, squeaks, and whistles with their wings likely evolved because it gave certain hummingbird species a selective advantage. For mating purposes, the sounds are an effective added element to visual courtship dances. The audible signals also benefit territorial defense and competition.
Interestingly, females of most hummingbird species do not vocally interact using their wings. This suggests the sounds play a specific role in male reproductive fitness displays. The fact that wing sounds are most pronounced during breeding season provides further evidence of their courting and competing function.
Mimicking the Sounds
The distinct wing sounds of hummingbirds have inspired musical instruments that seek to mimic their vocalizations:
- Aztec “Whistling Vessels” – Clay instruments that mimicked hummingbird sounds when air was blown through them
- Whistling jug toys – Designed to re-create hummingbird whistles
- Slide whistles – Musicians can produce sounds similar to hummingbird chirps on these instruments by manipulating the plunger
While man-made instruments can approximate some of the sounds, nothing can perfectly replicate the intricacy and fluidity of live hummingbird wing vocalizations.
Conclusion
The ability of some hummingbird species to produce chirping, squeaking, and whistling wing sounds provides an excellent example of how anatomical adaptations can evolve for effective visual and vocal signaling. Male hummingbirds appear to benefit during courtship and in defending territory by adding an audible element to their flight displays. The sounds serve as a mode of communication and competition during breeding season. While the aerodynamics allow for precision control of tone and pitch, the muscles to modulate wing position have evolved specifically for this display. The result is a unique vocalization ability that intrigues both ornithologists and casual birdwatchers alike.