Abstract: Metacognition refers to the ability to monitor and control one's own cognitive activities such as memory. Although recent studies have raised an interesting possibility that some species of nonhuman animals might possess such skills, subjects often required a numerous number of training trials to acquire the effective use of metacognitive responses. Here, five orangutans (Pongo pygmaeus) were tested whether they were able to escape spatial memory tests when they did not remember the location of preferred reward in a relatively small number of trials. The apes were presented with two identical cups, under one of which the experimenter hid a preferred reward (e.g., two grapes). The subjects were then presented with a third container, “escape response”, with which they could receive a less preferred but secure reward (e.g., one grape). The orangutans as a group significantly more likely selected the escape response when the baiting of the preferred reward was invisible (as compared to when it was visible) and when the hiding locations of the preferred reward were switched (as compared to when they remained unchanged). Even when the escape response was presented before the final presentation of the memory test, one orangutan successfully avoided the test in which she would likely err. These findings indicate that some orangutans appear to tell when they do not remember correct answers in memory tests.

Abstract: The papers in this special issue examine the relationship between social and ecological cognition in primates. We refer to the intersection of these two domains as socioecological cognition. Examples of socioecological cognition include socially learned predator alarm calls and socially sensitive foraging decisions. In this review we consider how primate cognition may have been shaped by the interaction of social and ecological influences in their evolutionary history. The ability to remember distant, out-of-sight locations is an ancient one, shared by many mammals and widespread among primates. It seems some monkeys and apes have evolved the ability to form more complex representations of resources, integrating “what-where-how much” information. This ability allowed anthropoids to live in larger, more cohesive groups by minimizing competition for limited resources between group members. As group size increased, however, competition for resources also increased, selecting for enhanced social skills. Enhanced social skills in turn made a more sophisticated relationship to the environment possible. The interaction of social and ecological influences created a spiraling effect in the evolution of primate intelligence. In contrast, lemurs may not have evolved the ability to form complex representations which would allow them to consider the size and location of resources. This lack in lemur ecological cognition may restrict the size of frugivorous lemur social groups, thereby limiting the complexity of lemur social life. In this special issue, we have brought together two review papers, five field studies, and one laboratory study to investigate the interaction of social and ecological factors in relation to foraging. Our goal is to stimulate research that considers social and ecological factors acting together on cognitive evolution, rather than in isolation. Cross fertilization of experimental and observational studies from captivity and the field is important for increasing our understanding of this relationship.

Abstract: Common cuckoos (Cuculus canorus) are obligate brood parasites, laying eggs into nests of small songbirds. The cuckoo hatchling evicts all eggs and young from a nest, eliminating hosts' breeding success. Despite the consistently high costs of parasitism by common cuckoos, great reed warbler (Acrocephalus arundinaceus) hosts sometime accept and other times reject parasitic eggs. To explore the cognitive basis of this seemingly maladaptive variation in host responses, we documented differences in egg rejection rates within 1-day periods just before and during the egg-laying cycle across host nests. Hosts rejected cuckoo eggs at 28% of nests during the pre-egg-laying stage, but when cuckoos exchanged the first host egg with the parasite egg, rejections increased to 75%. Even later, when several host eggs remained in a nest after parasitism, rejection rate fell to 37.5%. Experimental parasitism with conspecific eggs on the first and second day of host laying showed a similar directional change in relative rejection rates, dropping from 35 to 0%. Mistakes in egg discrimination (ejection error and ejection cost) were observed mostly in the latter part of the laying cycle, mainly when nests contained 5-6 eggs. These correlational and experimental patterns of egg rejection support a cognitive process of egg discrimination through several shifts in hosts' optimal acceptance thresholds of foreign eggs. The results are also consistent with the evolution of foreign egg rejection in the context of nest-sanitation (i.e. the removal of foreign objects). Our results suggest that common cuckoo hosts may recognize more eggs than they reject. This implies that the experience of the host with one or more of its own eggs in the clutch is a key factor in rejecting parasite eggs by allowing inspection and learning about their own clutch.