Most mammals, including people, see and hear in stereo. For instance, stereo vision means that we see an object in three dimensions.
But only a few mammals have been confirmed to have a stereoscopic sense of smell. That means that each nostril operates independently of the other, sending different signals to the brain that are then computed to determine the direction of the odor.
A previous study showed that rats could be trained to tell whether an odor came from the left or right. But the new study in moles is the first to show a mammal using this ability as part of its natural foraging behavior.
Biologist Kenneth Catania showed that the common mole—also known as the Eastern American mole—relies on the ability to distinguish between subtle differences in the intensity of smells at each nostril to locate food. (See "Secrets of Smell: Different Nose Parts for Stinky, Sweet.")
"I came at this as a complete skeptic. I didn't really think it was possible, partly because the nostrils are pretty close together," said Catania, who is at Vanderbilt University in Nashville, Tennessee.
The Dirt on Mole Vision
In one experiment, Catania placed a mole into a circular arena with food wells spaced around a 180-degree circle. Pieces of chopped earthworm were placed randomly in different wells. Catania then temporarily sealed the chamber so that he could detect each time the mole sniffed by the change in air pressure.
When a mole first entered the chamber, it sniffed the air, and in five seconds or less would zero in on the earthworm pieces. "It would wiggle its nose ... and then just go straight toward the food in what looks like a straight line," said Catania, whose research appears February 5 in the journal Nature Communications.
The definitive evidence that the moles rely on stereo sniffing came from yet another test. Catania inserted small plastic tubes in both of the moles’ nostrils and crossed them, so the right nostril was sniffing air on the animal’s left and the left nostril was sniffing air on the animal’s right. When their nostrils were crossed in this fashion, the animals searched back and forth and frequently could not find the food at all.