Pigeons consistently prefer easy over harder access to food: No reversal after direct dopaminergic stimulation

Many studies show that animals may prefer earned over free food-a phenomenon referred to as "contrafreeloading." In rodents, dopamine-which is involved in incentive motivation and effort-facilitates the occurrence of such a preference. Here, we investigated the behavioral effects of pramipexole (PPX), a dopamine D2/3 receptor agonist, on contrafreeloading in pigeons. In Experiment 1, 2 groups of pigeons (PPX and SAL) were simultaneously exposed to a bowl that contained grains only (easy food option) and a bowl that contained grains covered with sawdust (harder food option) for 6 sessions. They were tested in two treatment conditions (high vs. low amount of food available). In Experiment 2, the two groups of pigeons were first repeatedly presented with the harder food option (training phase, 6 sessions) and then with the two options at the same time (test phase, 3 sessions). In order to potentially increase the physiological effects of PPX, the dose was tripled, and there was a 2-week incubation of the drug between Sessions 3 and 4 at training. The results indicate that the pigeons from both groups preferred to forage on the easy food option, and PPX did not alter this preference. Despite indications that PPX was effective, its action consisted of reducing-rather than magnifying-the attractiveness of the harder food option. It is suggested that pigeons are less motivated to deploy foraging effort than rodents in similar tasks. (PsycINFO Database Record