Rats apparently have a nose for hunger: the rodents use olfactory clues to determine how urgently their peers need their help, according to a study. They feed hungry-smelling animals to eager food as those that exude a rich smell. The researchers also provide information on which volatile substances in the air the rats use to determine this difference. The smell information may enable the intelligent rodents to decide more objectively who really needs help, the scientists say.
Clever, compassionate and helpful: The behavior of rats and humans shows astonishing parallels, studies have documented in recent years. The intelligent rodents are ready to help fellow species, even if this does not immediately give them an advantage. They liberate imprisoned members of the same species or push food to them, even if they don’t get anything from it. A recent study also showed that rats shy away from causing pain to other species – even if this means that they do not need to be rewarded. Accordingly, rats seem to have empathy similar to humans – empathy.
Clever helpfulness
Earlier studies have also shown that the willingness to help of the rats has complex features: They decide on the basis of certain characteristics and behaviors of the other person how they show solidarity. The following applies: If a rat signals a need for help through gestures or sounds, it is more likely to be heard by its peers. However, as Karin Schneeberger from the University of Potsdam and her colleagues explain, these messages could lead to helpful animals being exploited. Because calls and gestures may not reflect an individual’s actual need for help. The scientists therefore asked themselves whether rats also use a more objective indication of their helpfulness – the smell.
To test this hypothesis, they conducted experiments with rat rats (Rattus norvegicus). A test system was used in which the test animals had previously demonstrated their willingness to help in principle. There are two animals, which are not known to each other, in side-by-side plexiglass containers that have a grilled side. Outside the bars there is a food tray that can be moved to the cages using an elongated pulling element. However, only one of the two rats can reach the pulling element with the paw and operate with force. This animal then does not reach the range of the feed, but only the neighboring rat. The preliminary experiments have shown that the experimental animals understand the connection and are prepared to provide the neighboring rat with unselfish food.
A nose for needy help
In order to investigate their current experimental question, the scientists blew air into the cage of the potential helper rat, which came not from her neighbor, but either from a saturated or from a hungry rat that was in a distant room. The evaluations of the behavior of the helper rats showed that the animals provided help three times faster on average when they picked up the odor signals from a hungry rat than from a full one. According to the researchers, these results confirm their hypothesis: the animals classify the degree of need of the conspecific on the basis of the olfactory information and then behave accordingly.
In further investigations, the researchers then investigated the question of whether a difference in smell between saturated and hungry rats can also be demonstrated analytically. To do this, they subjected the ambient air of the corresponding animals to an analysis using gas chromatography. They identified seven volatile organic compounds that distinguish the smell of hungry and full rats. However, where they come from remains unclear: As the researchers explain, they could come directly from the previously ingested food sources, but also from metabolic processes during digestion, or possibly from a pheromone that indicates hunger.
However, whatever the source – the smell is objective information that rats can rely on when they are ready to help, the scientists conclude.