Why Can Birds Hover in the Air Without Flapping Their Wings?
The Significance of Wings in Flight
Depending on their wing shapes, some birds need to flap their wings constantly to stay airborne, while others can glide or soar for minutes or even hours without frequent wing flapping.
How Bird Wings Help Them Move Forward
A bird’s wings create an airfoil. When a bird flies, the shape and curvature of its wings cause air to move faster over the top than below. This faster airflow above generates lower pressure, lifting the bird upwards, while the slower airflow below increases pressure, pushing the bird up. This upward force, known as “lift,” requires the bird to keep moving forward or face a strong headwind.
The shape of wings determines how birds fly
Albatross wings are characterized by their long and slender shape, featuring a high aspect ratio, enabling them to swiftly navigate at low altitudes (sometimes even skimming just above the waves) with exceptional agility. In contrast, vultures have broad wings with slots and a lower aspect ratio. Birds with low aspect ratio wings are adept at leisurely flying at higher altitudes. Those with wings at either extreme of the aspect ratio spectrum may find it challenging to take off from the ground without facing strong headwinds. The majority of soaring birds fall somewhere between these two extremes.
The Weight of Birds
To fly upward without flapping their wings, birds need a low body weight relative to their wing and tail surface area, resulting in low wing loading. Birds with low wing loading include cranes, eagles, vultures, anhingas, pelicans, and others. In contrast, loons have high wing loading, making their body weight heavy relative to their wing surface area. If loons lose just a few flight feathers, flying can become difficult or even impossible. Penguins are an extreme example of high wing loading; their small wings can’t generate enough lift to get their heavy bodies off the ground. Hummingbirds and some waterfowl also have high wing loading, requiring them to constantly flap their wings to stay airborne.
