The foraging behaviour of Mongolian gerbils: A behavioural need or a need to know?

In the present paper Mongolian gerbils (Meriones unguiculatus) were shown to prefer to forage from an unprofitable food source when it contained hidden food, but not when the food was clearly visible. Four experiments were performed, in each experiment the animal could forage from either a food source with easily accessible food or from a food source which required more work. In the first experiment the animal could choose between seeds with husks and those without, and in the second experiment between seeds glued to a stick and seeds in a bowl. In both these experiments the animals could see the food of both food sources. The animals chose to forage from the most profitable food source, i.e. the seeds without husks and the seeds in a bowl respectively. In the third experiment the animals could choose between earing seeds hidden under lids or seeds in a bowl, and finally in the fourth experiment they could forage for seeds on a camouflaging surface or on a surface where the seeds were clearly visible. In these last two experiments it was impossible to see the food in the unprofitable food sources without working for it. In these situations the animals choose to forage from the unprofitable food source, i.e. from underneath the lids and on the camouflaging surface. These results are in accordance with exploration being the driving force behind contrafreeloading (learned industrioussness). The results cannot be explained by classical optimal foraging theory.