Behavioural Variation in Echolocation Pulses of the Northern Bat, Eptesicus nilssoni

Abstract

Abstract17 northern bats, comprising a maternity colony, were observed and recorded in their natural feeding habitat in southern Sweden. They searched for insects in more or less open habitats, 2–50 m above ground, and usually established individual feeding territories, which were patrolled in straight or slightly curved flight paths at rather constant altitudes. Duration, bandwidth, amplitude, repetition rate and, to a lesser extent, terminal frequency of the echolocation pulses varied according to feeding habitat and situation. In general, long (13.0–17.7 ms), loud, shallow frequency‐modulated (FM) signals were used during search flight near treetop level (15 m) or above. At lower altitudes, steep FM‐components were added, and the terminal shallow‐sweep portions were shortened. These pulses were 6.3–13.4 ms long. Steep FM‐signals of short (0.4–8.4 ms) duration and relatively low amplitude were used in the vicinity of obstacles or targets.