ACQUISITION OF PINE CONE STRIPPING BEHAVIOUR IN BLACK RATS (Rattus rattus)

Abstract

Black rats (Rattus rattus) have begun occupying a new habitat in recent years—the Jerusalem pine (Pinus halepensis) forests in Israel. In this, otherwise almost sterile habitat, the sole source of nourishment for the rats is the pine seeds that can only be extracted from the cones through a complex feeding technique. Adult black rats un- familiar with the technique (termed naive) were unable to attain it either through trial and error or through observational learning when housed with experienced rats (termed strippers). In contrast, black rat pups raised by stripper mothers did learn the pine cone opening behaviour. In addition to the presence of a stripper model, however, the clues of the pine seeds themselves, as well as partially open cones, may also play a role in the acquisition of the technique. The state of the cone itself, when encountered by the rat pups, may be an important factor. Three groups of experimental animals were used: 25 pups born to naive mothers and reared on rat chow without exposure to either stripping mothers or partially opened cones; 25 pups born to naive mothers and exposed to pine cones in various stages of opening; 55 pups born to stripper mothers and exposed both to pine cones and to the presence of their mothers actively involved in stripping the cones and feeding on the seeds. We found that pine cone stripping behaviour is learned through two stages of a local enhancement effect: First, the pups are directed to the pine cones as a food resource, and then to the cone's proximal end as a starting point. The development of the stripping technique is acquired individually, with accumulating experience. Black rats (Rattus rattus) have begun occupying a new habitat in recent years—the Jerusalem pine {Pinus halepensis) forests in Israel. In this, otherwise almost sterile habitat, the sole source of nourishment for the rats is the pine seeds that can only be extracted from the cones through a complex feeding technique. The scales must be stripped from the cone in a sequential fashion in order to expose the underlying seeds, which are tightly organized around the shaft of the cone. The rat sys- tematically strips the scales one by one, following the spiral order around the shaft, until only the bare shaft remains (Aisner & Terkel, 1985).