Bats are unique mammals known for their sustained flight. They navigate diverse environments, from forests to open skies, for food or migration. While known for impressive horizontal speeds (e.g., Mexican free-tailed bats reaching 100 mph), bats also ascend to significant altitudes, an often-overlooked aspect of their aerial prowess.
The Heights Bats Reach
Bats occupy altitudes from near ground level to thousands of meters. The Mexican free-tailed bat (Tadarida brasiliensis mexicana) has documented flights exceeding 3,000 meters (nearly 10,000 feet). Other migratory bats, such as the North American Lasiurus cinereus, have been observed at altitudes up to 3,000 meters. In Europe, the European free-tailed bat (Tadarida teniotis) has been tracked climbing over 1,600 meters (approximately one mile), reaching 1,680 meters.
While some bats, like the big brown bat, typically fly around 30 feet (9 meters), others regularly forage at hundreds of meters. Open-space foraging bats in the Old World have been recorded flying over 800 meters. Even in challenging environments like the Central Alps, bats have been detected at altitudes exceeding 2,700 meters, operating even in thin air and low temperatures.
Reasons for Varied Flight Altitudes
Bats adjust their flight altitudes primarily to optimize foraging, commute, and avoid threats. Many species, particularly insectivorous bats, ascend to high altitudes to hunt migratory insects that utilize upper atmospheric layers. This high-altitude foraging is effective, as seen with Mexican free-tailed bats feeding on agricultural pests hundreds to thousands of meters aloft.
Migration is another reason for sustained high-altitude flight, allowing bats to cover long distances efficiently. Temperate bats often migrate altitudinally, moving between lower and higher elevations seasonally. Bats may also use higher altitudes for orientation. Ascending also allows navigation around obstacles or exploitation of favorable wind currents, minimizing energy expenditure.
Environmental and Species Factors
A bat’s ability to fly at certain heights is influenced by environmental conditions and biological characteristics. Air density, which decreases with altitude, is a factor affecting flight efficiency; lower density requires more energy for lift and thrust. Temperature, wind currents, and atmospheric pressure also play roles, with bats sometimes exploiting updrafts, like orographic uplift, to gain altitude with less energy. Some species can even fly in high winds and near-freezing temperatures.
Species-specific adaptations are important. Wing morphology, including wing shape and size, impacts how efficiently a bat can fly at different altitudes. Larger, fast-flying bats, like molossid bats, often have physiological adaptations such as higher hematocrit levels and slightly lower oxygen affinity, specializations for high-altitude flight. Body mass also affects flight performance; smaller bats generally have different flight characteristics than larger ones.
Researching Bat Flight
Scientists employ techniques to gather data on bat flight heights and behaviors. Radar tracking is a method, with weather radars, originally for meteorology, now monitoring large-scale bat movements. These radars can distinguish between birds, bats, and insects, providing long-term data on emergence and dispersal patterns. Specialized MERLIN radar systems track bats and birds, particularly around wind farms.
Acoustic monitoring is another technique, using specialized microphones to detect ultrasonic echolocation calls. Detectors can be placed at various heights to record bat activity, though recording high-flying bats is challenging due to signal attenuation. Miniaturized GPS tracking devices have improved the study of individual bat movements in three dimensions, revealing precise flight paths and altitudes, especially for larger species. These technologies help overcome challenges in studying these small, nocturnal creatures that often fly in difficult-to-observe aerial environments.