Bats are unique among mammals because they are the only group capable of true, sustained flight. This ability has allowed them to colonize nearly every habitat on Earth, resulting in over 1,400 diverse species. Because of this vast range in size, habitat, and lifestyle, bat flight speed is never a single number. Speeds vary dramatically depending on the species and the activity the bat is engaged in.
Average Cruising Speeds
The typical cruising speed for a bat during routine activities establishes a general baseline. For mid-sized North American species, sustained speed is modest, prioritizing efficiency and maneuverability. The Big Brown Bat (Eptesicus fuscus), common across the United States, typically maintains a cruising speed around 20 miles per hour (32 kilometers per hour).
Sustained flight differs from short bursts of speed used for immediate needs. While cruising, the Big Brown Bat can accelerate up to 40 mph (64 kph) when pursuing prey or evading a threat. Smaller species, such as the Little Brown Bat (Myotis lucifugus), are naturally slower, usually flying at about 12 mph (19 kph). Their maximum speed tops out around 22 mph (35 kph) due to their smaller size.
Even the Brazilian Free-Tailed Bat, known for its record potential, maintains a median flight speed closer to this average range during nightly commutes. The average speed for a bat in level flight generally falls within the 10 to 25 mph (16 to 40 kph) range. This speed allows for the efficient long-distance travel many insectivorous bats undertake.
Breaking the Speed Barrier
The fastest bat is the Brazilian Free-Tailed Bat (Tadarida brasiliensis), also called the Mexican Free-Tailed Bat. This species has been documented achieving maximum ground speeds of up to 100 mph (161 kph) during horizontal flight. This velocity is significantly faster than any previously documented speed for a bat or a bird in level flight.
These speeds were scientifically confirmed using advanced tracking technology, not mere estimates. Researchers attached tiny, half-gram radio transmitters to the backs of individual bats using surgical glue. An airplane followed the complete flight path as the bats emerged from their roosts, allowing for precise measurement of ground speed.
The study emphasized that the bats reached these extreme velocities without the assistance of a tailwind or a dive. This high-speed performance is possible due to the bat’s unique physical characteristics. They possess a sleek, streamlined body and long, narrow wings, a morphology known as a high aspect ratio optimized for straight-line speed and open airspace.
Biological and Environmental Influences on Flight
A bat’s speed is dynamic, resulting from its biology and the surrounding environment. Wing morphology is a primary determinant, as the shape of the wing dictates the bat’s aerodynamic capabilities. Bats that fly long distances or hunt in open air, like free-tailed bats, have long, narrow wings that facilitate high speeds.
Conversely, species that forage in cluttered environments, such as forests, have shorter, broader wings with a lower aspect ratio. This design sacrifices straight-line speed for superior maneuverability and the ability to make rapid, tight turns. Another factor is wing loading (body mass divided by total wing area); bats with higher wing loading generally fly at higher velocities.
The environment also plays a role in moment-to-moment adjustments. Bats actively regulate their air speed in response to wind conditions, much like human-engineered aircraft. They increase their flapping speed when flying into a headwind to maintain a desired ground speed, and conversely, slow their flapping when benefiting from a tailwind. Furthermore, the bat constantly adjusts its wing kinematics, changing the wing area, the angle of attack, and the camber (curvature) of the wing membrane to fine-tune lift and drag.