Among songbirds, the type of sounds they make vary depending on the habitat. According to Sandra Vehrencamp, professor emerita at The Cornell Lab of Ornithology, a trilling sound doesn’t carry well through heavy vegetation. So those that trill tend to live in marshy areas and grasslands, where there is less interference. Birds that live in forests and jungles emit warbles and whistles instead, which are less susceptible to echo. Similarly, the ground can absorb high-pitched sounds, so birds that skitter in the underbrush tend to use low, whistling sounds. The songs of musical wrens, which live near the rainforest floor, sound like flutes.