17 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.