FIG. 1. Call spectrograms for B. barbastellus close to the roost. A) Standard pass echolocation, showing lower frequency type 1 and higher frequency type 2 pulses alternating, then followed by type 1 pulses only; B) Approach echolocation pulse group produced by a single bat approaching the roost tree entrance. In each case, pulse analysis was based on the central group of five pulses: pulses 3 to 7 from the left in this case. This example shows a group of lower frequency pulses on the far right, typical of a bat approaching the tree very closely; C) Swarming echolocation recorded with two bats in flight close to the roost. These are broadband pulses with second harmonics. Pulses do not appear in a fixed pattern as with approach echolocation, but tend to be produced in a dynamic group. It is not possible to determine from which bat successive pulses originated; D) Swarming honking recorded with five bats in flight round the roost tree. These are similar to swarming echolocation pulses but with a high amplitude quasi-constant frequency (QCF) tail, apparently to communicate with bats on a collision course; E) Hooked social calls recorded just before swarming activity with five bats. The straighter pulses next to the hooked calls were presumably produced by a different bat