Hummingbirds are remarkable little birds that capture the imagination with their speedy flight and hovering capabilities. A hummingbird’s wings beat incredibly fast, flapping on average about 50 times per second. This rapid flapping produces the characteristic humming or buzzing sound that gives hummingbirds their name. But why exactly do hummingbird wings make this sound when they beat so fast? There are a few key reasons.
Resonance of feathers
One factor is the resonance of the feathers. Hummingbird wing feathers are fairly stiff and narrow. As air flows rapidly over the feathers during the downstroke, the feathers vibrate at high frequencies like reeds in a wind instrument. This causes them to resonate, amplifying the underlying tone of the wingbeats. The resonance allows the wing hum to be audible to human ears. Slower flying birds like pigeons do not achieve the same resonant effects.
Size of wings
The small size of hummingbird wings also contributes to the hum. Hummingbird wings are only around 3 to 4 cm long. They flap through relatively large angles of motion at high speeds. The short length allows the wings to flap back and forth very quickly through the air. The fast oscillating motion of such small wings generates the high frequencies that we hear as a hum. Larger wings on bigger birds cannot beat as rapidly due to greater inertia, so do not hum in the same manner.
Speed of flapping
Of course, the high flapping frequency itself is key to the humming sound. An average rate of 50 flaps per second generates considerable air turbulence as the wings continuously slice through the air. In physics, any periodic or cyclical motion at high enough speeds tends to produce an audible tone. The extremely rapid oscillations of a hummingbird’s wings create vibrations in the surrounding air that our ears interpret as a hum. Slower wingbeats would not stimulate sounds at such high frequencies.
Functions of wing hum
The humming or buzzing sound is not just an incidental byproduct – it likely serves some important functions for hummingbirds.
Stabilization during hovering
Hummingbirds hover frequently when feeding on flowers. Studies show their wings make a louder hum when hovering compared to forward flight. The noise seems to help stabilize their position. As the wings hum, they set up oscillations in the air that act like inverted pendulums. This allows more precise control and hovering balance. Attenuating the wing hum reduced hovering accuracy in experiments.
Communication
The volume and pitch of the humming likely also facilitates communication. Hummingbirds produce diverse sounds with their wings and tails during courtship rituals and aggression. The wing hum enables them to signal their presence from a distance. Females may even select mates based on subtleties of the male’s hum. Dominant males warn others away from their territory using menacing hums.
Hummingbird species | Wingspan | Wingbeat frequency (flaps/sec) |
---|---|---|
Bee hummingbird | 5-6 cm | 200 |
Anna’s hummingbird | 8-10 cm | 62 |
Rufous hummingbird | 8-9 cm | 53 |
Calliope hummingbird | 7-8 cm | 80 |
Defense through intimidation
The noisy hum can also deter potential predators. To some small birds or insects, the loud, fast hum imitates the sound of a much larger predator such as a wasp or bee. This may provide safety through deception. Many creatures avoid the area when they hear the ominous hum of hummingbird wings.
Mechanics of hum production
On a biomechanical level, several attributes of hummingbird anatomy and flight create the right conditions for humming.
Specialized shoulder joints
Hummingbirds have a ball-and-socket shoulder joint that permits extensive rotational movement. This allows the necessary wing articulation to produce thrust on both the downstroke and upstroke. Other birds primarily generate lift only during the downstroke. By utilizing both strokes, hummingbirds flap faster.
Rotating wings
Specialized bones and joints also enable hummingbirds to rotate their wings during each stroke. This keeps the wing oriented at an ideal angle. The rotating wings stay aerodynamically efficient even at high frequencies, enabling the sustained rapid flapping.
Large chest muscles
Up to 30% of a hummingbird’s total body weight is flight muscle contained in their enlarged chest. With substantial power in a compact body, they can flap quickly without overexerting themselves. The large muscle mass also lets them hover for extended periods.
Lightweight build
Hummingbirds are extremely lightweight for their size. Their feathers, bones, and other structures are finely adapted for efficiency. This diminishes the energy required for flapping at high speeds. A heavier bird would overheat and tire too quickly at the same wingbeat frequency.
Wing loading concept
Wing loading is an aerodynamic parameter that helps explain hummingbird flight and hum. It quantifies how much weight is supported by a given wing area. Hummingbirds have remarkably high wing loading ratios compared to other birds.
This means each square centimeter of their small wings supports more grams of body weight. To generate enough lift, they must flap faster, increasing wing velocity and hum pitch. Hovering demands even higher wing loading and flapping rates, resulting in the loudest hums.
High wing loading benefits
The high wing loading gives hummingbirds some key advantages:
- More agile maneuvers
- Ability to exploit scattered food sources
- Hovering stability near flowers
- Endurance migrating long distances
But it comes at the cost of requiring high energy expenditure and near-continuous feeding. This is why hummingbirds visit hundreds of flowers daily and consume up to 8 times their body weight in nectar each day.
Disadvantages of high wing loading
The high wing loading and flapping rates also introduce some flight challenges:
- Difficulty flying in rainstorms
- Higher risk of overheating
- Demanding hover-feeding
- Limited gliding ability
To meet the demands of their small, overloaded wings, hummingbirds have numerous anatomical and metabolic adaptations for their extreme lifestyle.
Evolution of specialized hummingbird flight
Hummingbird flight mechanics reflect an evolutionary journey millions of years in the making. Tracking archaeological evidence reveals when and how they diverged from swifts and developed their unique abilities.
30 million years ago
Ancestors of modern swifts and hummingbirds split off from other birds. Primitive versions of key traits like short wings, aerodynamic bodies, and wide mouthparts slowly emerged.
10 million years ago
Further specialization continued. Ancestors grew longer, thinner beaks suited for probing flowers. Partial hovering ability appeared but not sustained for feeding.
Period | Evolution of flight adaptations |
---|---|
50 million years ago | Ancestors had basic swift-like wings and bodies |
30 million years ago | Differentiation from swifts began |
10 million years ago | Partial hovering ability developed |
3-5 million years ago | Complex hummingbird flight originated |
3-5 million years ago
The most advanced energetic flight adaptations rapidly evolved. Shoulder joints pivoted, wing muscles enlarged, feathers stiffened, bones lightened, and wing rotation emerged, culminating in continuous hovering.
Incredible flight facts
To further appreciate the unique flight and sounds of hummingbirds, consider these incredible facts:
– Hummingbird wings beat on average 50 times per second, but can reach 200 times per second during display dives.
– Their heart rate exceeds 1,200 beats per minute and oxygen consumption per gram is the highest of all vertebrates.
– Ruby-throated hummingbirds weigh only 2-4 grams but migrate 500 miles nonstop over the Gulf of Mexico.
– Hummingbirds hover in place by generating enough lift to support their weight on the upstroke and downstroke.
– Male Anna’s hummingbirds produce loud wing trills during breeding displays by vibrating their outer tail feathers near 100 times per second.
– Hummingbird tail shapes, forkedness, and spread help stabilize and steer their nimble bodies.
– They can fly forwards, backwards, upside down, loop in circles, and hover motionless in defiance of gravity.
– Wind tunnel tests show hummingbird wings are less efficient at slower speeds, lending advantages to their high flapping rates.
Threats and conservation
Though captivating, hummingbirds face serious threats that require conservation actions to ensure thriving future populations.
Habitat loss
Destruction of forests and meadows for development removes crucial feeding and nesting habitat. Hummingbirds depend on native plant species that are often the first eliminated.
Pesticides
Chemicals applied to lawns and agricultural areas accumulate in the environment. Trace amounts can poison hummingbirds and contaminate pollen and nectar.
Climate change
Changing climate patterns disrupt migration timing and food availability.Extended droughts can kill flowers and trees hummingbirds rely on.
Collisions
Reflective glass buildings and homes disorient hummingbirds and cause deadly collisions during migrations. Outdoor cats also prey on hummingbirds at feeders.
How you can help
– Plant native flowers and trees that provide nectar and habitat.
– Avoid pesticides in your yard to build a safe haven.
– Install screens on windows to prevent collisions.
– Keep cats indoors and use deterrents to protect hummingbird feeders outside.
– Support groups like the Audubon Society that lobby for bird protections.
Conclusion
Hummingbird’s wings hum because of rapid flapping that sets up high frequency resonant vibrations in their stiff, shortened feathers. The sound is amplified by their small size and extreme wing loading. The energetic hum facilitates hovering stability, communication, and defense. Millions of years of aerial evolution shaped their incredible anatomy leading to specialized energetic flight. But human activity now threatens these captivating birds. By understanding the wonder of hummingbird wings, we can better appreciate nature’s engineering and build motivation to provide the conditions these amazing creatures need to thrive.