Predator odor exposure increases food-carrying behavior in rats

To cover their energy demands, prey animals are forced to search for food. However, during foraging they also expose themselves to the risk of becoming the prey of predators. Consequently, in order to increase their fitness foraging animals have to trade-off efficiency of foraging against the avoidance of predation risk. For example, the decision on whether a found food piece should be eaten at the food source or whether it should be carried to a protective site such as the nest (food-carrying behavior), is strongly dependent on different incentive factors (e.g., hunger level, food size, distance to the nest). It has been shown that food-carrying behavior increases the more risky the foraging situation becomes. Since predator odors are clearly fear-inducing in rats, we ask here whether the detection of predator odors in close proximity to the food source modulates food-carrying behavior. In the present study, the food-carrying behavior of rats for six different food pellet sizes was measured in a "low risk" and a "high risk" testing condition by presenting water or a fox urine sample, respectively, next to the food source. For both testing conditions, food-carrying behavior of rats increased with increasing food pellet weight. Importantly, the proportion of food-carrying rats was significantly higher during exposure to fox urine ("high risk") than when rats were tested with the water control ("low risk"). Taken together, these results demonstrate that food-carrying behavior of rats is increased by the detection of a predator odor. Our data also support the idea that such food-carrying behavior can be considered as a pre-encounter defensive response.