Carrying behavior in synanthropic rats
Technical note on carrying behavior in synanthropic rats, with a focus on diagnosis, prevention and criteria applicable to professional pest management.
When rats discover food, they seek to transport it protected to eat it without incident. This behavior is called carrying. The article delves into some of its aspects.
The feeding behavior of synanthropic rats is one of the most controversial aspects of their biology. Although the topic has been the subject of numerous investigations, many of them were based on conditions in which certain behaviors are substantially modified. Among them, one of the most sensitive to the limitations imposed by captivity is the transportation of food.
Rattus rattus and Rattus norvegicus Not only do they use the burrow to nest, sleep or take shelter, but they also accumulate various components of their diet there with the ultimate goal of ingesting them in spaces that provide security.
In general, the issue can be raised by saying that when an animal finds food, it does not eat it in that place, but rather usually moves it to some protected place before eating it. This behavior is called carrying.
One of the points of greatest controversy revolves around the discussion about whether carrying is developed uniformly by all members of the colony or if, on the contrary, it is related to the status of those individuals. In this regard, Calhoun suggests that the inclination to carry is particularly intense in the specimens most vulnerable to attack by their conspecifics. That is, the socially subordinated.
Our personal observations coincide with what this author stated. In an established colony, dominant males never carry food to the burrow. On the contrary, whenever they want to, they go to a food source and eat there for periods of three or four minutes. Juvenile, subordinate individuals, on the other hand, generally appear extremely fearful; The approach to food is much more hesitant and once they make contact with it, they quickly seek to transport it to the burrow.
It is known that individuals from lower social strata are attacked by the dominant ones when they interfere in the exploitation of a resource. Taking this into account, the presence of a subordinate for many minutes at a food source would make him the recipient of an attack if a dominant decided to feed at that time. In this sense, carrying could be interpreted as a way to minimize permanence in a food source and thus reduce the possibility of being the target of aggression.
On the other hand, a situation little described in the available literature, and that we were able to frequently observe, is that carrying reaches its maximum expression in postpartum females. In fact, the volume of food carried by them is immensely greater than what they are capable of ingesting.
What purpose does this excessive activity of females contain? A viable answer could be elaborated from the fact that, once accumulated in the nest, the food is ingested not only by it, but also by its young.
Although the collective intake of food within the burrows is a common situation, carrying would be enhanced by motherhood as a way of providing food for the litter. This would be confirmed by an additional observation: during the first excursions out of the nest, at 18-20 days after birth, the chicks never eat solid food despite following the mother to the food source. Therefore, everything seems to indicate that this behavior of the juveniles would be related exclusively to the exploration of the environment and not, as some researchers maintain, to the search for food, which is ingested inside the burrow after having been carried by the mother.
In a simplified way, it could then be said that the carrying would be conditioned by the social status of the individual or that, seen another way, it would be the product of individual experience.
Although many aspects of this behavior still remain to be known, it is clear that carrying is an extremely complex activity that should not be interpreted simply as a stage within the ingestion sequence. The unknowns about the true dimension and the specific purposes that promote the development of hauling mean that a big question still remains: how does this behavior influence the efficiency of rodenticide baits?