“Don’t be late for your weekly mud bath!” — Pigs can estimate time intervals in the range of days
We can all agree that pigs are astonishingly clever creatures. They possess excellent spatial memory skills, remembering not only multiple feeding sites but also whether they’ve visited them recently. When foraging in groups, dominant pigs often exploit the knowledge of lower ranking pigs regarding the location of food sources that the dominant pig is unaware of. Subordinate pigs have also been shown to subsequently apply ‘anti-exploitation’ strategies such as being more cautious when close to dominant group members and only moving towards food when they are out of sight or cannot see them. But do pigs actually know how much time has passed since they last visited a food source or scrounged off another pig? Remembering when you last visited your favourite acorn tree might come in handy as depleted food sources can replenish over time and are thus worth a second look in the future.
New research now sheds light on pigs’ ability to estimate such time intervals. To do this, the researchers conducted two experiments; one focusing on estimating intervals of a few minutes, while the second one focused on intervals of several days. In the minute-experiment, pigs were equipped with a heart rate monitor device and could feed freely at a trough. During a training phase, they learned to expect an interruption while feeding at a trough after a fixed interval of a few minutes. In the actual test, this interruption was delayed and the researchers observed how the pigs reacted around the time the initial interruption would have occurred. Heart rate measurements and behavioural indicators, such as head lifts and food stamps, showed that the pigs became continuously more aroused towards the end of the interval. However, they did not show a sharp reaction at the moment the interruption would have occurred, and actually showed the greatest reaction some seconds after the disturbance would have been expected. Due to this, instead of estimating the time interval, it’s possible the pigs were simply following a rule of thumb such as monitoring their level of satiety or the amount of food they had already eaten.
In the day-experiment, the pigs were introduced individually to a test pen from which they could choose to enter two additional pens. The pigs needed to learn that a low-quality reward was offered in one pen every other day and a high-quality reward in the other pen every fifth day. After intense training, pigs were increasingly more likely to open the door leading to the high-quality reward on the correct (5th) day, but not so on days in which entering the pen wouldn’t have yielded a reward. The authors concluded that their pigs could estimate time intervals in the range of days, but had problems estimating time intervals in the range of minutes. These results complement a previous study, which showed that mini pigs demonstrate episodic-like memory skills, i.e. they remember not only what happened at which location, but also when a specific event happened in temporal comparison to another event.
To remember and recall previous events and estimate time intervals has a major impact on an individual’s capacity for suffering and thus is of interest to researchers aiming to improve animal welfare. For instance, if an animal perceives the length of time during which it remains in a negative situation, its suffering could be inflated. This effect could be even further exacerbated if animals can remember and foresee such events. But the ability to estimate time intervals could also be used to counter negative conditions by signalling their duration to the animal via, for example, acoustic cues. The ability to estimate such time intervals could, therefore, result in both welfare benefits and problems.
The current finding that pigs are able to estimate time intervals adds to a body of fast growing literature on the cognitive capacities of pigs. In fact, these findings are desperately needed, as it is of great importance to know how pigs, and farm animals in general, perceive their environment in order to adapt husbandry and management conditions to their needs. So remember: the next time you arrange a meeting with your favourite pig at the petting zoo, be aware that it expects you to be on time.