Stereotyped active sensing in fast-diving echolocating bats.

Mexican free-tailed bats (Tadarida brasiliensis) often return to their roosts in darkness or low-light conditions from high altitudes (>3 km) during steep, fast dives. We recorded 26 bats as they performed reentry dives to their canyon roost in New Mexico shortly after dawn and analyzed their sensorimotor behaviors. We tracked bats at altitudes up to 25.6 m above the ground; they dove at maximum speeds of 22.1 m/s (82.1 km/h), experienced forces up to 9.2 g, and traversed distances of up to 6 m (∼60 body lengths) between receiving echoes from the ground. Bats adjusted their echolocation in a stereotyped pattern once the ground was within detection range by decreasing signal duration, shortening interpulse intervals, and increasing signal end frequency. Our analyses suggest that bats receive relatively sparse echo information during dives and likely integrate this information with cognitive spatial maps and available visual cues to safely complete their high-speed roost reentry.