Smelling in stereo

Moles are practically blind, but they make up for it by smelling in stereo. Most mammals, including humans, see and hear in stereo, but smelling in this fashion has been demonstrated in only a few animals.
In order for an animal to smell stereoscopically, its two nostrils have to work independently, each sending a separate signal to the brain. The brain combines the signals and calculates the direction of the scent.

This effect was investigated at Vanderbilt University in Nashville (USA) by a scientist who, at first, was very sceptical. He didn’t think it was possible, because the animal’s nostrils are so close together, that the mole could be determining the location of food with stereoscopic smell. The experiment began by placing small food wells in a semicircle. For each trial, a number of the wells was filled with chopped earthworm. When the mole entered the chamber, it sniffed briefly and then found the food within five seconds. ‘The mole would wiggle its nose and then go straight towards the food’, the investigator reported.

In the next experiment, one nostril was blocked with a small plastic tube. With the right nostril blocked, the moles veered to the left when seeking food; with the left nostril blocked, they veered to the right. Next, the nostrils were ‘crossed’ using the plastic tubes, so that air from the right was perceived as coming from the left, and vice versa. The moles then kept moving back and forth in search of the food. Although it took them longer to locate the food this way, the moles were eventually still successful in finding it; apparently, these animals are not completely dependent on their stereo sense of smell.

Smelling in stereo is important not only in finding food, but also serves to perceive the presence of predators—and the ability to locate the enemy with a single sniff could save an animal’s life.