A key topic in foraging ecology is whether a particular prey type is consumed because it is more abundant or easier to catch, or because there is a specific preference for it. The great tit Parus major is an ideal species for studying this topic. Although it is traditionally regarded as a caterpillar specialist, in certain periods, e.g. during the breeding season, or areas, such as the Mediterranean forests, the great tit seems to show a preference for spiders. We conducted food choice experiments with captive birds to ascertain which of these two main prey types (caterpillars vs. spiders) was preferred outside the breeding season when there was an opportunity to prey on both food types. In conclusion, we found that, regardless of any variation in the supply-demand ratio and the amount of food available, Mediterranean great tits showed a preference for spiders.