Pigs Are Terrible Game Theorists

February 5, 2019

At first glance feeding time for the older pigs is a classic zero sum game. There’s a limited amount of grain, and when it’s gone there won’t be any more until tomorrow. So it’s up to each sow to scarf as much as possible and to do it quickly.  What’s remarkable is the extent to which something like curiosity or jealousy makes such incredibly gastrocentric animals really, really bad at doing this.

My pigs are in two groups at the moment. There are the growers, which were born last fall. They have access to a free feeder, meaning they can all eat as much as they want, day or night, and so they don’t concern us here. The other group consists of our boar and sows. In mature pigs there’s a mismatch between what they want to eat and what they should - left to their own devices they would devour a prodigious amount of grain, which would be unhealthy for them and expensive for me. So I give them hay to munch on whenever, but they only get one limited grain feeding each morning.

Because pigs have a loose hierarchy, if all the feed went into a single tub only one or two would eat most of it, while the smallest would be left with nothing. To avoid this I spread the grain out, so it’s in more tubs than there are pigs. And this is where things get interesting. It doesn’t take an advanced mathematical model to figure out that the most efficient course of action would be for each pig to pick a tub, empty it as quickly as possible, and only then go looking for more. But this is precisely the opposite of what happens. Below is a diagram of what they should do.


Understandably, the pigs all go crazy for the first pile of grain, snorting and squealing while they  push each other around. But as soon as I start putting feed in other places around the paddock they head to each in turn, choosing to examine each new scoop collectively. When all the grain is distributed they’ll disperse a bit, but even then they won’t just settle down to eat. Instead, they’ll take a few mouthfuls, then run off in search of another tub. Often the first tub I put feed in is the last to be finished.

This would maybe make a little bit of sense if it was only the boar and the largest sows that did it, since they could theoretically be looking for the fullest troughs, confident that they could push away a smaller pig. But this is not the case. All of them do it. The littlest, youngest sow will abandon a nearly full tub and start running around looking for something else just as frequently as her larger peers. So the reality looks more like this:


This is why I think jealousy is the best analogy for the behavior. It must be motivated by a concern that some other pig has found something better, a concern so powerful that all the pigs continually act on it to their own individual detriment. (Actually, it probably shakes out evenly, since they all engage in this behavior, but if one would simply settle down and eat she’d easily get a disproportionate amount of grain.)

It’s also another opportunity for me to question pigs’ vaunted intelligence. The routine is identical day after day. None of the troughs ever secretly have higher quality feed in them. The best strategy is obvious, and it’s easier - it would take less effort for them to simply eat what was in front of them, rather than charging all over the place taking a bite here and another there. But the thought that they might against all odds be missing out on something makes them unable to simply apply themselves to the thing right in front of their snouts.

(Stunning original artwork by Garth Brown.)

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