Hummingbirds are amazing little birds that have mastered the art of hovering in place. Their ability to hover while drinking nectar from flowers is one of the characteristics that makes them unique. But why do hummingbirds hover? What allows them to stay suspended in mid-air without flapping their wings constantly?
What is hovering?
Hovering refers to the ability of hummingbirds to stay suspended in one place while their wings are beating very fast. It allows them to maintain a fixed position relative to a flower from which they can extract nectar.
During hovering, the wings of a hummingbird beat in a figure-eight pattern. The wings rotate at the shoulder to allow both an upward and downward stroke. This creates enough lift to counteract gravity and keep the bird suspended without moving forwards or backwards.
Why do hummingbirds hover?
Hummingbirds hover for two main reasons:
- To feed from flowers – Hovering allows hummingbirds to maintain a stable position relative to a flower, so they can insert their beak and extract the nectar efficiently.
- To conserve energy – Hovering takes less energy than flapping wings while moving. So if a hummingbird doesn’t need to move, hovering burns fewer calories.
Hummingbirds have evolved the ability to hover specifically as an adaptation for feeding from flowers. Other birds cannot hover nearly as well as hummingbirds can.
How do hummingbirds hover?
Hummingbirds are anatomically and physiologically adapted in several key ways that enable them to hover:
Wing anatomy
- Their wing bones and muscles are specialized to enable the wings to rotate at the shoulder socket.
- Their wings can beat up to 80 times per second – much faster than other birds.
- The shape of their wings creates sufficient lift with a small surface area.
Lightweight bodies
- Hummingbirds are the smallest birds – they weigh only 2-20 grams.
- Their lightweight skeletons and minimal body fat allow them to hover using less energy.
High metabolism
- They have incredibly high metabolisms and consume up to twice their body weight in nectar daily.
- The high intake of calories provides the massive amounts of energy needed for hovering.
Hovering adaptations
In addition, hummingbirds have anatomical and physiological adaptations that maximize their efficiency at hovering:
- Enlarged breast muscles for powerful wing strokes.
- Rotatable wrists to control wing movement.
- Excellent eyesight to maintain position mid-air.
- Specialized feathers that reduce noise and turbulence.
- Controlled breathing synchronized with the heartbeat.
All of these adaptations allow hummingbirds to hover with a high degree of stability and control.
How much energy does hovering take?
Hovering is an extremely metabolically expensive activity. Hummingbirds expend a lot of energy to stay suspended in one place.
During hovering flight, hummingbirds consume energy at a rate of 60 to 70 kilojoules per hour. This is approximately 10 times higher than their basal metabolic rate at rest.
To put it into perspective, if humans had a similar energy expenditure per gram of body weight, an adult man would consume over 140,000 calories per hour when hovering!
Due to their small size and specialized adaptations, hummingbirds are estimated to hover with about 20-40% efficiency in converting metabolic energy into mechanical power for flight. Still, they must consume up to half their body weight in nectar daily to meet their energy needs.
Oxygen consumption
The oxygen consumption of hummingbirds also skyrockets during hovering. Studies have found that their oxygen consumption rises by 34x compared to rest. This massive increase powers their accelerated metabolism and wing muscles during hovering.
Wing-beat frequency
The wings of hummingbirds beat incredibly quickly during hovering flight. Average wing-beat frequency increases to 40-80 beats per second, compared to non-hovering flight at around 12 beats per second.
Maintaining very rapid wing oscillations requires tremendous energy expenditure. But this is necessary to generate enough lift to counteract gravity.
How long can hummingbirds hover?
Despite their specialized adaptations, hummingbirds are only able to sustain energetically expensive hovering flight for brief periods of time.
During feeding, hummingbirds will hover in place for 30-60 seconds at a time. They then must perch and rest for energy recovery.
Longer hovering periods have been observed when hummingbirds are attracted to artificial feeders. In this situation, they have been recorded hovering in place for 2-3 minutes, likely because they don’t have to expend extra energy moving between multiple real flowers.
However, this is still a tiny fraction of their normal active period during the day. Hummingbirds can only afford to spend 5-10% of their total time hovering. Any longer and they risk starvation due to the massive energy drain.
Differences among hummingbird species
There are over 300 species of hummingbirds throughout the Americas. They vary somewhat in their innate hovering abilities.
For example, the Bee Hummingbird is the smallest species in the world, weighing only around 2 grams. It also beats its wings up to 200 times per second during hovering! This allows it to hover remarkably well despite its tiny size.
On the other hand, hummingbird species adapted to higher elevations may not hover as efficiently. At higher altitudes, the lower air density provides less lift for a given wing speed. These species compensate by having broader wings to increase lift.
Males and females may also differ – male hummingbirds tend to be smaller and better adapted for hovering around flowers. Females spend more time gathering food for their offspring and don’t hover as frequently.
The differences highlight that hovering energetics depend on both body size as well as ecological factors that shape a species’ adaptations.
Hovering in slow motion
Here is a slow motion video that lets you see the complex mechanics of hummingbird hovering flight:
Key observations:
- The rapid figure-eight wing movement that provides lift.
- The wings rotating at the shoulder socket to maximize thrust.
- The precision required to maintain position.
- The sheer speed of the wing oscillations.
This incredible maneuver is what enables hummingbirds to feed so effectively from flower nectar.
Why don’t other birds hover as well?
Hummingbirds are uniquely adapted for hovering compared to other bird species. Most birds cannot hover for more than a brief second or two.
There are two main reasons why other birds don’t hover:
Energy demands
The metabolic demands of hovering flight are extremely high. The vast majority of birds simply cannot consume enough calories to generate the required energy.
Hummingbirds have the highest metabolism of any animal relative to their size. This enables them to take in enough nectar calories to meet their energy needs.
In contrast, similarly sized insects can hover very well, because they need less total energy and can get that from sugars in flower nectar.
Body size
Larger birds weigh too much for their wings to sustain hovering. The heavier body mass generates more gravitational force than their wings can counteract.
Hummingbirds weigh only 2-20 grams on average. Their tiny size is key to hovering, since less lift and thrust are needed to overcome gravity.
Larger birds like crows or hawks would need much higher wing power output and pectoral muscle strength to achieve hovering flight.
Amazing ubiquity of hummingbird hovering
Despite the metabolic demands, hummingbirds hover frequently because it maximizes their foraging efficiency.
A hummingbird will hover dozens or hundreds of times per day as it feeds on flower nectar across their territory.
This ubiquitous hovering behaviour is facilitated by their specialized energetic, anatomical, and biomechanical adaptations.
Other birds simply cannot afford such frequent and sustained hovering bouts. But for hummingbirds, it’s essential to thriving in their ecological niche.
The next time you see a hummingbird effortlessly hovering at a flower, remember the incredible evolution that enables this marvellous sight!
Conclusion
In summary, hummingbirds are exceptional among birds for their ability to hover in mid-air for sustained periods of time. They can do this because of numerous anatomical and physiological adaptations that enable them to generate sufficient lift and thrust to counteract gravity, while also meeting the extreme metabolic demands.
These adaptations include specialized shoulder joints and wing musculature, an extremely high metabolism and oxygen consumption, and ideal body mass. Hovering provides hummingbirds with an efficient means to feed on flower nectar.
The marvel of hummingbird hovering flight reflects an evolutionary fine-tuning to their ecological niche. Their hovering capability is unique in the animal kingdom and should be appreciated for its biomechanical wonder.
