Hummingbirds are remarkable little birds capable of hovering mid-air and flying forwards, backwards, up, down, and sideways with ease. Their unique wings allow them to perform aerial acrobatics that fascinate ornithologists and bird enthusiasts alike.
Anatomy of hummingbird flight
Hummingbirds have specially adapted wings that enable them to fly with precision in any direction. Here are some key features of their wings:
- Their wings can beat up to 80 times per second, allowing for finer manipulation of their flight.
- They can rotate their wings in a full circle, enabling them to fly backwards.
- Their shoulder joints are highly flexible, allowing their wings to move in any plane.
- They have asymmetric wings, with the left wing larger than the right. This helps them stabilized their bodies during hovering.
In addition to their unique wings, hummingbirds have proportionally large chest muscles (up to 30% of their total body weight!) which provide the powerful wingstrokes necessary for hovering and flying in multiple directions.
Hovering
Hummingbirds are the only birds that can fly backwards. This is because of their specialized ability to hover mid-air. Hovering requires that they beat their wings in a figure-eight pattern and angle them on both the upward and downward strokes. This creates forward, backward, and sideways forces that allow them to precisely hold their position even in gusty conditions.
Here are some key facts about hummingbird hovering:
- They beat their wings 12-80 times per second while hovering. The Anna’s hummingbird has the fastest known wingbeat at 80 times per second.
- Their wings rotate at the shoulder joint more than 180 degrees during each stroke while hovering. This allows them to generate both forward and backward force.
- They can alter the angle of their wings to produce torques that rotate their body mid-air. This allows them to orient themselves when hovering in order to track flowers or insects.
- Hovering is the most energetically expensive form of flight due to the power required. A hovering hummingbird may consume more than twice as much energy as one flying forward.
Flying backwards
Few birds can match the aerial maneuverability of hummingbirds. When hovering, they can generate backward force by angling their wings appropriately on both the upstroke and the downstroke.
Here are some key points about backward flight in hummingbirds:
- Backward flight requires wing angles of attack between 50-70 degrees on both downstroke and upstroke to generate rearward aerodynamic forces.
- During backward flight, the downward stroke provides about twice as much rearward thrust as the upward stroke.
- Hummingbirds primarily use backward flight for precision positioning when feeding from flowers. It allows them to maintain access to nectar while adjusting orienation.
- Male Anna’s hummingbirds have been observed flying backwards at speeds over 10 m/s during mating dives as they ascend after diving past females.
- Backward flight is slower than forward flight given the physiological limitations. The maximum speed is about one third of their maximum forward speed.
Researchers have used sophisticated techniques like particle imaging velocimetry to study the wake vortices generated during hummingbird flight. These studies reveal how hummingbirds can reorient their lift forces for omnidirectional control while hovering.
Manoeuverability in forward flight
Hummingbirds can fly forwards like any other bird by tilting their bodies and flapping their wings. However, they have exceptional control over their flight:
- They can fly precisely through dense, cluttered spaces to reach flowers.
- They can fly sideways or even upside down for brief periods.
- Their relatively short wings allow extremely fast rotations for tight turns.
- They reflexively adjust their wings to gusts and turbulence for stability.
- Their flight muscles make up 20-35% of their body weight, giving them the stamina for sustained flight.
Hummingbirds achieve their remarkable maneuverability through supracoracoideus muscles that allow them to change wing stroke angle and plane. They can tilt their stroke angle over 100 degrees giving fine control over torques on their body.
Forward flight speeds
In forward flight, hummingbirds can reach impressive speeds:
- Maximum speed records are around 60 mph (96 km/h) during courtship dives. However, normal flight is slower.
- Cruising speeds while migrating are typically 25-30 mph (40-48 km/h).
- Their average speed while feeding is around 5-10 mph (8-16 km/h).
- The smallest hummingbirds have higher wingbeat frequencies and are more maneuverable than larger ones.
- Ruby-throated hummingbirds can reach up to 54 body lengths per second in courtship flight.
Researchers study hummingbird flight using specialized high speed cameras that can capture up to 10,000 frames per second. Detailed tracking of the birds in free flight reveals the complex aerodynamics that enable these tiny masters of the air.
Role of tails
Hummingbirds have small tapered tails that they actively control in flight to increase agility:
- They fan and angle their tails horizontally to remain balanced in hovering flight.
- Rapid fanning of the tail provides yaw control. This enables precise side to side movements.
- The tail also acts as a rudder for steering in forward flight.
- Fanning their tail feathers increases drag on one side, causing them to orient in that direction.
- They splay their tail to generate aerodynamic forces for braking at high speeds.
Research shows hummingbirds coordinate tail spreading with their asymmetric wing strokes to control flight. High speed videos reveal how the tail works in conjunction with wing angles for stability and steering.
Role of feathers
Hummingbirds’ light, flexible feathers enable their specialized flight:
- Their feathers make up only 5-7% of their weight, the lowest ratio in birds.
- Their feathers have fewer interlocking barbules, giving more flexibility and movement.
- They can actively control their feathers, changing the camber (curvature) during each stroke.
- They lack down feathers for insulation since they can more easily trap heat while flying.
- Their wingtips have specialized fringed and notched feathers that reduce turbulence and stall.
High speed microscopy of hummingbirds in flight shows their feathers morphing shape. PhD student Bret Tobalske at the University of Montana captured magnified video of this microsecond-scale feather movement during hovering.
Slow motion analysis
Analyzing slow motion videos provides insights into hummingbird flight mechanics:
- Thousands of frames per second are needed to study details due to their rapid wingbeats.
- Particle imaging tracks airflow patterns surrounding the wings during forward, hover, and backward flight.
- The videos reveal leading edge vortices spiraling over the wing at different angles of attack.
- Oscillations of feathers are visible as they dynamically change shape during each stroke.
- Subtle adjustments in wing angle relative to the stroke plane are observable using frame-by-frame analysis.
Understanding these dynamics helps explain the aerodynamic forces enabling hummingbirds’ aerial agility and efficiency. The research also aids engineers in designing micro drones that mimic bird flight.
Unique adaptations
Hummingbirds have many unique evolutionary adaptations for flight:
- Their wings connect to their body near the base, allowing great flexibility and control.
- They have ball-and-socket shoulder and hip joints for rotating their limbs biaxially.
- They have reduced number of secondary flight feathers for lightness and maneuverability.
- Their light skeleton makes up only 4% of their body weight.
- They have excellent eyesight to see flowers, feeders, and predators while flying.
- They have fringing on wing feathers to dampen turbulence and reduce drag.
These specializations enable hummingbirds’ unrivaled hovering stability, mobility, and endurance. Research continues exploring how they squeeze every advantage out of their tiny bodies.
Energetics of flight
Hummingbird flight is extremely energetically demanding:
- Hovering costs about 10 times more energy than resting. This requires consuming up to their body weight in nectar daily.
- Their flight muscles account for 20-35% of their weight to provide enough power.
- Their heart rate can reach as high as 1,200 beats per minute during flight.
- They respire through their avian flow-through breathing system to supply oxygen.
- They can starve within hours if they cannot regularly feed on nectar for energy.
- To conserve energy overnight, they enter torpor, lowering their metabolism by 50-95%.
Given their extreme energetics, hummingbirds carefully budget their flight time. Hovering in front of flowers just long enough to lick nectar reduces unnecessary energy expenditure.
Neurological control
Hummingbirds have evolved sophisticated neurological control of their flying abilities:
- Special neural sensors measure air flowing over their wingtips to detect stall conditions.
- Their brain integrates visual, vestibular, and proprioceptive information to tightly control position.
- They have the largest hummingbird brains relative to their body size to handle the complex coordination.
- Built-in reflexes automatically compensate for gusts or perturbations to maintain stability.
- They can remember detailed feeding locations and precisely return to favorites.
- Their color vision and spatial memory guide them to red tubular flowers.
Research decoding hummingbird brains is revealing how flying acrobats monitor and correct their flight motor output for precision maneuvering.
Implications for robotics
Studying hummingbirds provides bioinspiration for designing robotic aircraft:
- Their hovering ability helps engineers create more agile micro drones.
- Imitating their flexible wings and feathers can improve drone efficiency.
- Understanding their sensing and stability can aid algorithms for autonomous flight in complex environments.
- Replicating their maneuvers requires advances in flapping mechanisms and aerodynamics.
- Applying their energy efficiency can extend flight times for small drones.
- Mimicking their brains can enable drones to learn optimal flight control policies.
Groups like Festo have built robotic hummingbird prototypes that mimic bird flight with various degrees of fidelity. Advancing these bioinspired designs remains an active area of aerospace research.
Conclusion
In summary, hummingbirds possess unique flying abilities unmatched by other birds. Their specialized wings, muscles, and energetics enable them to hover mid-air, fly in any direction including backwards, and rapidly accelerate and turn. Understanding the biomechanics, energetics, and neuroscience behind their flight reveals fascinating evolutionary adaptations. Their supreme aerial agility continues inspiring roboticists seeking to engineer increasingly maneuverable micro drones.