Wing form and flying strategies -

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Wing form and flying strategies

About mammals > Adaptations for flight

The wing forms of bats are highly variable from species to species. A particular form (e.g., either long and narrow or short and broad) may reveal a relationship between flight style and foraging habits because it is likely that selection pressure favors the evolution of the best wing form for a particular feeding style. The two primary quantities used for comparing wing morphology to flight style are wing loading (WL) and aspect ratio (AR). WL is the ratio of body weight to the surface area of the wing, which demonstrates the size of the wing relative to the size of the bat. In general, the higher the WL, the faster the bat has to fly to generate sufficient lift with relatively small wings.

One calculates AR by squaring the wingspan and dividing that number by the wing’s surface area. AR measures the broadness of the wing. The higher the AR, the narrower and more aerodynamically efficient (lower drag) is the wing. Bats with high-AR wing morphology are faster flyers, but lack the agility of bats with low AR. The surface areas of the uropatagium and the plagiopatagium are large in slow, agile flyers because these areas provide most of the lift during flight. The propatagium alters the leading edge curvature of the wing, and prevents stalling during steep-angle flying. If the surface areas of these regions are large compared to the wingspan, giving a low AR, the agility of the bat is very high. Examining the wing form can provide clues about the bat’s specialization in foraging. There are no exact correlations because bats are very adaptable and highly flexible in their foraging habits.

Also, the wing form suitable for a certain foraging style may be a disadvantage in other aspects of bat behavior. Generalizations must be made with caution. With that in mind, observers have noted that some tendencies do emerge. In general, bats with wings having high WL and high AR are bats that fly fast and forage in open air above vegetation. These bats regularly fly long distances in a short amount of time, feeding on insects while in flight. Bats with wings having low WL and low AR are able to fly slowly without stalling and can make tight maneuvers.

They are gleaners and hoverers, able to navigate in heavy vegetation and to take off from the ground while carrying heavy prey. Fruiteating bats that forage among vegetation and carnivorous bats that catch prey from the ground both fit in this category. High-WL and low-AR wings tend to belong to bats that fly fast, but have short, broad wings and are capable of maneuvering in cluttered spaces. They tend to be expert hoverers, and their flight speed allows them to visit among separated patches of vegetation in a minimum amount of time. They also tend to specialize in nectar or pollen feeding. Low-WL and high-AR wings are found among fishing bats that fly slowly over open water with very little tight maneuvering required. The low body weight allow these fishers to carry off the day’s catch for later consumption.

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