High Altitude Flights of the Free-Tailed Bat, Tadarida brasiliensis, Observed with Radar

Both search and height-finding radars were used to observe the airborne behavior of free-tailed bats, Tadarida brasiliensis mexicana, near several caves in the southwestern United States. Radar echoes from dense groups of bats covered areas as large as 400 square kilometers and rose to altitudes of more than 3000 meters. The presence of large numbers of bats within these areas was confirmed by visual observation from a helicopter. Bat flights appeared on radar at dusk and at dawn as a slowly expanding or contracting target, usually located near a known roost. The direction in which the echo expanded most rapidly was not due to drift of the bats by winds. This leading edge often moved at more than 40 kilometers per hour, indicating the capacity for rapid, well-directed, high altitude flight in these animals. Bats flying at such high altitudes must employ sensory systems other than echolocation for orientation and navigation.