Temporal dynamics of echolocation during clutter navigation in Eptesicus fuscus

The echolocating big brown bat, Eptesicus fuscus, must both avoid background objects that it may collide with such as vegetation or clutter, and identify insect prey targets. When bats fly through clutter, they emit groups of echolocation sounds in rapid succession called strobe groups. Here, we investigate the limitations of strobe grouping for flight guidance during clutter navigation. We hypothesized that as clutter conditions become extreme, bats will be no longer able to use strobe groups to navigate. We exposed bats to our laboratory flight room cluttered with plastic chains—obstacles that are acoustically similar to vegetation. Bats flew down a corridor 1.0 m wide, 0.7 m wide, or 0.4 m wide, and echolocation sounds were recorded with a 22-microphone array. We used a means clustering analysis to quantify inter-pulse intervals (IPIs) as belonging within a strobe group or between strobe groups. We found that bats made significantly more sounds per flight as the corridor width decreased. Strobe groups in the wide condition contained longer within-strobe IPI, while strobe groups in the narrowest condition had the shortest. We also investigated how many sounds per strobe group were used. These results show a relationship between clutter density and the temporal structure of echolocation calls.