Rats Sniff Out Hunger and Share Food With Each Other Based On Need, Study Finds

A study of rats suggests that the animals share food with each other based on need, sniffing out cheaters by using their sense of smell.

Rats are known to share food with each other, basing decisions on need and the costs and benefits of sharing. Visual, auditory and other cues are used to indicate hunger and solicit food donations from fellow rats. The new study, published Tuesday in the journal PLOS Biology and conducted by researchers in Germany and Switzerland, found that the rats verify hunger levels based on odor.

The study identified seven distinct organic chemicals that are present in rats in varying levels depending on hunger. The study's authors suggest that a "smell of hunger" can be detected by rats, which provides a potentially "honest cue" and helps the rats determine whether a seemingly needy compatriot is truly hungry.

"Rats seem to use the partner's inadvertent smell of hunger as a reliable indicator for its current need, adjusting their helping propensity accordingly," the study states. "Honesty is enforced because of physical, developmental, or physiological constraints that cannot be cheated."

Two rats drinking
Rats share food with each other based on need that is verified by "the smell of hunger," according to a study published on March 24, 2020. Getty

Although rats are known to commonly share food with each other and tend to benefit from their charity through reciprocation, the study showed that the animals leapt to the aid of rats that smelled genuinely hungry faster than those who seemed to be faking.

The study focused on Norway rats, also known as common or brown rats, but the authors noted that reciprocal sharing of food has been observed in several animal species.

Vampire bats are known to regurgitate blood from prey and then share it with fellow bats who hunted unsuccessfully, and odor could play a role in determining which bat was in need. Smell could also play a role in elephants signalling each other to take part in cooperative tasks.

Newsweek reached out to one of the study's authors for comment but did not receive a response in time for publication.

Rats have a highly tuned sense of smell, being able to detect a wide range of odors and chemicals and determine the direction the odor is coming from in only milliseconds. In addition to the typical olfactory system, the noses of rats contain a second organ used to detect smells, called the vomeronasal organ.

The additional organ helps rats and other animals receive signals like pheromones, chemicals that can cause changes in behavior among members of the same species. The vomeronasal organ has also been detected in some humans but is nonfunctional and thought to be a vestigial remnant of evolution.