Rats are more generous when they sniff the smell of hunger

March 25 (UPI) -- Rats can smell hunger, according to a new study. The research showed rats are more generous when exposed to the odor of hunger. The phenomenon suggests rats use odor cues to prioritize care and assistance for rats in need.

Norway rats, Rattus norvegicus, are one of many species known to reciprocally exchange food. The rodents are capable of calculating the cost of assistance, as well as the potential benefit to the recipient.


While rats regularly use calls and gestures to seek food assistance from their peers, this form of communication can be manipulated. To find out whether odor might serve as a more "honest" cue, scientists in Switzerland and Germany designed a series of lab experiments.

Researchers exposed rats to the odors of both starved and nourished rats in separate containers. The rats were provided a mechanism with which to provide food to their neighbor. When exposed to the smell of hunger, rats were more likely to push the food tray toward their neighbor in need.

Scientists described the experiments and results this week in the journal PLOS Biology.

"By using a variant of the sequential iterated prisoner's dilemma paradigm, we show that rats may determine the need of another individual by olfactory cues alone," researchers wrote.


"Rats donate food preferably to social partners in urgent need," scientists concluded.

After studying the effects of smell on rat behavior, scientists analyzed the chemical properties of the air surrounding both hungry and well-fed rats. They found differences in the abundance of seven volatile organic chemicals.

Researchers can't yet be certain whether the process of metabolizing food produces volatile compounds that produce the smell of satiation -- with the "smell" of hunger being the absence of such compounds -- or if a lack of food cues the production of putative pheromones.

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