The ability for birds to hover in one place is quite fascinating. Hovering requires a bird to generate enough lift to counteract gravity and remain stationary in the air. Several unique adaptations allow certain bird species to achieve this feat. In this article, we’ll explore what hovering is, which birds can hover, the adaptations that enable hovering flight, and the advantages of being able to hover.
What is hovering?
Hovering refers to the ability to stay suspended in one place while airborne. It requires precise coordination between a bird’s wings and body position to maintain altitude without moving horizontally. The wings must beat fast enough to generate upward lift equal to the bird’s weight. At the same time, subtle adjustments in wing angles and body posture counteract any drifting in the horizontal plane. This delicate balancing act allows hovering birds to stay fixed in the air.
True hovering requires the generation of lift equal to at least 100% of the bird’s weight. Many species can achieve near-hovering flight, flapping their wings vigorously while minimizing horizontal motion. However, any forward drift indicates they are not generating quite enough lift to fully counteract gravity.
Hovering is metabolically demanding since the wings must beat constantly to create sufficient lift. As such, most birds can only hover for short periods before needing to rest. However, some highly adapted species can sustain hovering flight for extended durations.
Which birds can hover?
While most birds are incapable of true hovering, some groups have evolved special adaptations to hover. The most adept hovering birds come from the following families:
- Hummingbirds
- Swifts
- Hoverflies
- Nectariniidae (sunbirds and spiderhunters)
- Trochilidae (hummingbirds)
Within these families, some specific examples of birds capable of hovering include:
- Anna’s Hummingbird
- Allen’s Hummingbird
- Rufous Hummingbird
- Calliope Hummingbird
- White-throated Hummingbird
- Ruby-throated Hummingbird
- Black-chinned Hummingbird
- Rufous-tailed Hummingbird
- Broad-tailed Hummingbird
- Eurasian Hobby
- Common Swift
- White-collared Swift
- Chimney Swift
- Pacific Swift
- Oriental Dollarbird
- Common Kingfisher
- Pied Kingfisher
- Laughing Kookaburra
- Palestine Sunbird
- Purple Sunbird
- Collared Sunbird
- Orange-tufted Sunbird
In general, smaller birds are better adapted for hovering. Their higher wingbeat frequency allows them to generate the required lift. Larger birds struggle to beat their wings fast enough to hover. The largest birds able to hover are swifts and hummingbirds, weighing around 20 grams (.7 oz) on average.
Adaptations for hovering
Hovering birds share some key adaptations that enable them to stay fixed in mid-air:
Small body size
A small, lightweight body enables hovering in two key ways. First, a lower body weight means less lift is required to counteract gravity. Second, small birds have a higher wingbeat frequency. Their smaller wings can flap faster compared to larger wings. Faster flapping translates to greater lift production.
High wingbeat frequency
Hovering birds have extremely high wingbeat frequencies, often around 50 beats per second. Flapping their wings so rapidly generates substantial lift. Hummingbirds achieve the fastest wingbeats of any bird, up to 80 beats per second.
Large pectoral muscles
The pectoralis major is the main muscle that powers the wingbeats required for flight. In hovering birds, this muscle makes up 15-25% of their total body weight. The large power-generating pectoralis allows them to beat their wings vigorously at high frequencies.
Lightweight skeleton
Minimizing body weight is critical for hoverers. They have lightweight skeletons lacking heavy minerals like calcium. Replacing bones with rigid protein provides structural support without the excess weight.
Reversed sexual size dimorphism
In most bird species, males are larger than females. However, in many hovering birds, the females are larger. Being smaller and lighter aids males during energetic hovering flight such as courtship displays.
Short tails and wings
Hovering birds have short broad wings and stubby tails. Short wings allow for faster flapping. Short tails reduce drag and weight, also enhancing lift production.
High metabolism
Hovering flight demands vast amounts of energy. To sustain it, hovering birds have very high metabolic rates. They can generate up to 10 times more energy per gram of body weight than non-hovering birds.
Unidirectional breathing
To feed their intense metabolism, hummingbirds have a unique breathing system. Their lungs can extract oxygen during both inhalation and exhalation. This unidirectional breathing provides a more constant oxygen supply during hovering.
Advantages of hovering
Despite its challenges, hovering provides several key benefits:
Foraging versatility
Hovering allows birds to exploit food sources unavailable to other species. Hummingbirds can lick nectar from each flower while buzzing insects can pluck prey from leaves and branches.
Expanded habitat range
By accessing more diverse food sources, hovering birds can occupy a wider range of habitats. For example, hummingbirds thrive in forest edges that offer both flowers and insects.
Precise maneuverability
The precisionflying of hoverers allows them to navigate cluttered environments. Hummingbirds can dart between branches and swifts contour their bodies into narrow crevices.
Energy efficiency
Counterintuitively, hovering demands less energy than flapping during slow, forward flight. Hovering is more efficient at slow speeds below 10 mph (16 kph).
Visual communication
Hovering enables unique visual displays. Hovering male hummingbirds can flash their iridescent plumage to attract mates.
Conclusion
In summary, hovering provides a range of benefits but requires specialized adaptations. Rapid wingbeats, small bodies, and efficient muscles allow certain birds to generate enough lift to counteract gravity. Hovering enables unique foraging abilities, expanded habitats, agile flight, visual displays, and efficiency at slow speeds. While metabolically taxing, this remarkable ability allows birds like hummingbirds and swifts to thrive.
