Military aircraft under enemy missile attack may use a variety of strategies to escape. There is, of course, the strategy of executing an evasive maneuver to avoid or disrupt the incoming missile. The aircraft may also use a variety of electronic signals to jam or fool the missile's sensor and tracking computer. These electronic strategies fall under the general category known as electronic counter measures (ECMs). As usual biology has its own incredible, organic, version of such technology. In the case of the bat and moth encounter, it is being elucidated by some excellent research.
Many bat species have a phenomenal biosonar, or echolocation, capability used to track insects. As they fly they may emit hundreds of ultrasonic squeaks per second. The squeaks are frequency-modulated and at frequencies in the hundreds of kilo Hertz. During the pursuit the bat shortens its squeaks and increases the transmission rate as it closes on the prey. In the terminal stage the bat rapidly adjusts its trajectory and posture to capture the insect. The return echoes are passed through a range-compensated automatic gain control to reduce signal strength variations during closure. The result is a tracking capability that is several times more accurate than our best military equipment.
While executing these tracking and intercept functions the bat is performing a complex signal processing task. For instance, the bat can discriminate the prey from background clutter. It also has a sort of synthetic aperture technology with which to construct image information. And it also uses complicated geometrical calculations to solve an advanced guidance scheme, as it closes on the target.
And what about the prey? Often on the receiving end of this carbon-based interceptor is the lowly moth. Some moths, however, sport their own battery of impressive capabilities to counter the bat's onslaught. They are not only able to hear the bat's ultrasonic squeaks, they also can perform complex, aerobatic escape maneuvers, and some moths even counter the bat's squeaks with their own ultrasonic reply. [1] These designs are not simple, and while years of excellent research have elucidated much of the details, many of the complexities have yet to be fully understood.
1. Barber JR, Conner WE, "Tiger moth responses to a simulated bat attack: timing and duty cycle," J Exp Biol, 209:2637-50, 2006.
