Cats can hear ultrasound to enhance their ability to detect high-frequency sounds produced by rodents which communicate in the 20-50 kHz range (mouse squeaks). Small cats are therefore well-equipped to detect the sounds of their prey.
Ultrasound is sound waves with frequencies higher than the upper audible limit of human hearing. The upper limit for human hearing is in the 15-20 kHz range. Cats can hear in the 65-70 kHz range.
The ear pinnae (ear flaps) of cats are like directional amplifiers increasing hearing sensitivity and allowing cats to pinpoint more accurately the position of prey. The serval is the best exponent of this characteristic as they are known to have huge dish-like ears to “sound hunt” small mammals in tall grass; their principle prey item.
The small wild cat species, the sand cat, is a good example as well. This cat has huge ears with large tympanic bullae which clearly demonstrates that this mammal relies on sound for detecting prey. The sand cat operates in sparse cover and its ear are therefore set low to enable it to take advantage of what cover it can find.
The cat’s brain compares differences in sound between the left and right ear which enables the animal to more clearly pinpoint the source. Higher frequencies are muffled by the time they reach the ear farthest from the source which also provides extra information as to where the sources is (Dr John Bradshaw Cat Sense). Cats can detect whether a a sound is coming from the right or left.
With respect to ultrasound from a mouse, for example, the “phase differences become too small to be useful, but the muffling effect gets larger and therefore becomes more informative” (Cat Sense).
It has to be mentioned too that the external parts of a cat’s ear are extremely mobile as most cat owners are aware. Cats have 32 muscles controlling their ear pinnae. Domestic cats often listen to us with their head turned away with their ears pointed backwards. This looks ‘impolite’ but is normal for cats.
The cat’s hearing is better than ours in many ways. However, Dr John Bradshaw says that it is less good in its ability to distinguish minor differences between sounds in pitch and intensity.