Hearing is an amazing biological and physical process. The average human can hear in the range of 20 Hz to 20,000 Hz (kHz). Normal adult hearing usually cuts off between 10-12 kHz, while children and teenagers can hear into the "mosquito" range of 14-18 kHz.
How do we compare to other creatures? A dog's hearing depends on its breed and age, but dogs can generally hear in the range of 40 Hz to 60 kHz, while bottlenose dolphins hear tones within the frequency range of 1 to 150 kHz. Wow!
Most bats need super sensitive hearing to make up for their poor eyesight particularly when hunting insects. Their hearing range is between 20 Hz and 120,000 Hz. A bat makes a very loud, short sound and assesses the echo when it bounces back. They use this echolocation to navigate and find food.
So next time you're surprised when something swoops down near you (e.g., mosquito, bat, etc.) remember, it was probably making sounds long before it arrived, you just couldn't hear them.