Caption: "A depiction of a bat, its ultrasound call, and the echo from an object."

As is well known, bats use echolocation help navigate: the time delay of the echo allows them to determine distances.

Slightly less well known is that they use of the Doppler effect for sound with echolocation. They emit high-frequency sound and judge relative speeds based on the frequency of the echo---and they don't need any formulae---just megayears of evolution (see Wikipedia: Echolocation: Doppler effect).

See Bat videos below (local link / general link: doppler_effect_bat.html):

Bat videos (i.e., Bat videos):

1. bat sounds - noises screeches and calls | 0:46: Look at those bat---the intricate fine structure. Pretty fun and short enough for the classroom.
2. BATS SOUND EFFECT IN HIGH QUALITY | 0:21: Just sound, no film.
3. Lens of Time: Bat Ballet | bioGraphic | 7:39: Greatest bat video ever!!!!

Credit/Permission: Petteri Aimonen, 2009 / Public domain.
Image link: Wikipedia: File:Animal echolocation.svg.
Local file: local link: doppler_effect_bat.html.
File: Waves file: doppler_effect_bat.html.