An interesting observation from this line of work (based on other articles in the area): the silence of owl flight depends on the frequency of the sound. Mice

An interesting observation from this line of work (based on other articles in the area): the silence of owl flight depends on the frequency of the sound. Mice have a range of frequencies that they can hear. If you line up the two curves, you can see evolution in action. Owl flight becomes quieter just at the low end of the sound frequency that mice can hear.