Crackbills (and other "Terror Birds", and crocodiles) hunt by listening for the low-frequency sounds of heavy footsteps. Add 2+ ranks of Enhanced Senses (Hearing).
http://www.livescience.com/50443-terror ... ecies.html
Given its extraordinary condition, the fossil has helped researchers study the terror bird's anatomy in detail. The specimen is the first known fossilized terror bird with a complete trachea and complete palate (the roof of the mouth). It even includes the intricate bones of the creature's ears, eye sockets, brain box and skull, providing scientists with an unprecedented look at the flightless bird's sensory capabilities.
An analysis of L. scagliai's inner ear structures suggests the terror bird likely heard low-frequency sounds, an advantage for predators that hunt by listening for the low rumble of their prey's footsteps hitting the ground, the researchers said. The new findings also suggest that the terror bird communicated using low-frequency noises, the researchers added.
"That actually tells us quite a bit about what the animals do, simply because low-frequency sounds tend to propagate across the environment with little change in volume," said Lawrence Witmer, a professor of anatomy at Ohio University who has worked with Degrange before, but was not involved in the new study.
"Low-frequency sounds are great for long-[distance] communication, or if you're a predator, for sensing the movements of prey animals," Witmer told Live Science.
This skill puts L. scagliai in good company. Other animals that can or could hear low-frequency sounds include Tyrannosaurus rex, crocodiles, elephants and rhinos, Witmer said.