Steering by echolocation: a paradigm of ecological acoustics

Abstract

• 1. Flights of three big brown bats (Eptesicus fuscus) landing on a hand and catching a suspended mealworm were video analysed.

• 2. Results were consistent with the bats using the same basic control procedure in the quite different approach tasks — namely keeping τ(r) = k _rand τ(a)τ(r) = k _αr. Here r is the current distance to the destination; α is the angle between the current direction of the destination and the goal direction of final approach (β _min); τ(r) = r/r, $\tau (\alpha ) = \alpha /\dot \alpha$; and k _r, k _αr are constants.

• 3. The bats were each quite consistent on a particular task (hand or mealworm) in the values they used for the control parameters k _r, k _αrand β _min. However, different values were used in the two tasks, which reflected the different behaviour required at the destination. Flights to hand required twisting and landing upside down and approach angle β _min was closer to vertical and k _rwas smaller and corresponded to decelerating nearly to a stop. In contrast, the mealworms were caught in mid flight and approach angle β _min was shallower and speed of approach was about constant.

• 4. τ(r) might be registered acoustically by τ(echo-delay) or by τ(echo-intensity). τ(α) might be registered by the bat's directional hearing and gravity sense.

• 5. The bats learned the tasks easily, suggesting that the control procedure they used in the experiments was part and parcel of the natural skills they had developed in the wild.