Domestic dogs and cats, like their wild, hunting relatives, rely heavily on their sense of smell and hearing to locate prey and danger, and to communicate. Cats and dogs are able to hear a wider range of sounds, and softer sounds than humans. The pitch of a sound is measured in Hertz (Hz) and the comparative hearing ranges of dogs, cats and humans are the following:

• Humans: 20Hz – 23 KHz
• Dogs: 60Hz – 45 KHz
• Cats: 45 Hz – 64KHz

To give you a practical example of this: 64Hz (roughly the lowest note a dog can hear) is the pitch of the lowest key on a piano. For every doubling in Hz, the pitch goes up an octave. Cats, with the top range of 64KHz vs 23 in humans, can thus hear sounds at least two and a half octaves higher than humans can! This is why dogs and cats respond to dog whistles. The sound is too high for us to hear, but still within their hearing range.

As a matter of interest, the animals said to hear the lowest sounds are elephants and ferrets (12 Hz) and the animal capable of hearing the highest sound is the Beluga whale (120KHz!)

Cats and dogs also respond to a much lower intensity of sound than humans. Sound intensity is measured in decibels (dB). Dogs can hear five times more acutely than humans, and cats about twice as acutely as dogs. Like Hz, dB also increase exponentially, so 30dB is ten times as loud as 20dB, and 40dB is 100 times as loud. A practical example is that a whisper weighs in at about 30dB, and a dog can hear that from almost three times as far away as a human. Cats are even more sensitive than dogs to these soft sounds. This also explains why dogs and cats are so scared by the sound of fireworks which, to us, do not seem so loud. They are in fact at least 5 times louder to our pets!

The sense of smell is related to the number of olfactory cells adapted to receive smell molecules, and to the area in the brain dedicated to processing these signals into recognisable smells. Humans have about 5 million olfactory epithelial cells, cats 100 million and dogs up to 220 million cells! The acuity of smell is proportional to these cells, so cats can smell roughly 20 times better than humans and dogs up to 50 times better! A scent dog can detect one drop of human blood in a bucket of water! The number of olfactory cells is partly dependant on the size of the animal’s nose. Small terriers have space for only about 120 million olfactory cells and brachycephalic (flat-nosed) dogs like bull-dogs even fewer. This explains, why German Shepherds, not Bull dogs, do tracking work!

Cats and dogs, however, use their sense of small far more specifically than to smell blood. Both species have a vomero-nasal organ, capable of detecting pheromone molecules. These are too large for normal olfactory epithelial cells to detect, so humans cannot smell them, but they transmit incredibly detailed information to the animals. Pheromones can transmit what mood an animal is in, whether it is on heat or pregnant and even if it is ill. Pheromones are like fingerprints for every animal. Placed against the relatively bland ability of humans to detect “something that smells like an apple”, it is not surprising that some people say dogs can smell a million times better than humans! As with hearing, they not only smell the same things we do, better, but they also smell things that we simply cannot.

ANIMALS IN FOCUS thanks Dr Marianne de Vries of the Department of Companion Animal Clinical Studies at the University of Pretoria’s Faculty of Veterinary Science for permission to reproduce this article.