Means-end comprehension in four parrot species: explained by social complexity.

A comparative approach is required to investigate the evolutionary origins of cognitive abilities. In this paper, we compare the performance of four parrot species, spectacled parrotlets (Forpus conspicillatus), rainbow lorikeets (Trichoglossus haematodus), green-winged macaws (Ara chloroptera) and sulphur-crested cockatoos (Cacatua galerita triton) in standardized string-pulling and string-choice paradigms. We varied the spatial relationship between the strings, the presence of a reward and the physical contact between the string and the reward to test different cognitive skills requiring means-end comprehension. The species tested showed a high individual and inter-specific variation in their ability to solve the tasks. Spectacled parrotlets performed best among the four species and solved the most complex choice tasks, namely crossed-string task and broken-string task, spontaneously. In contrast, macaws and cockatoos failed to identify the correct string in these two tasks. The rainbow lorikeets were outperformed by the parrotlets, but outperformed in turn the macaws and the cockatoos. The findings can be best explained by the variation in social complexity among species, rather than in their ecology.

Vocal sharing and individual acoustic distinctiveness within a group of captive orcas (Orcinus orca).

Among vocal learners, some animal species are known to develop individually distinctive vocalizations, and others clearly learn to produce group signatures. The optimal vocal sharing hypothesis suggests that vocal divergence and convergence are not compulsorily exclusive and both can be found at different levels in a given species. Being individually recognizable is socially important even in species sharing vocal badges. Acoustic divergence is not systematically controlled as it can simply be due to interindividual morphological differences. We tested that hypothesis in a species known to learn their family vocal dialect socially: the orca (Orcinus orca). We identified 13 different call types, including some shared by all group members, some shared only by 2 or 3 individuals, and others particular to 1 individual. Sharing was higher between males than between females. Three of our 4 orcas each produced a unique call type, which was preferably emitted. The call types shared by all orcas still presented individual acoustic distinctiveness that could, to some degree, be explained by morphological differences. We found evidence for strong similarities between some of the call types of our captive orcas and the call types of their ancestors, which are Canadian and Icelandic free-ranging orcas. Our findings suggest that captive orcas use a complex vocal repertoire enabling each individual to produce sounds that are similar to some of their partners', which might be used as social badges to advertise their preferential bonds, as well as individual-specific calls. Our findings open new lines of research concerning the functional value of a balanced "diverging-converging" vocal system.

Big brains are not enough: performance of three parrot species in the trap-tube paradigm.

The trap-tube task has become a benchmark test for investigating physical causality in vertebrates. In this task, subjects have to retrieve food out of a horizontal tube using a tool and avoiding a trap hole in the tube. Great apes and corvids succeeded in this task. Parrots with relative brain volumes comparable to those of corvids and primates also demonstrate high cognitive abilities. We therefore tested macaws, a cockatoo, and keas on the trap-tube paradigm. All nine parrots failed to solve the task. In a simplified task, trap tubes with a slot inserted along the top were offered. The slot allowed the birds to move the reward directly with their bills. All but one individual solved this task by lifting the food over the trap. However, the parrots failed again when they were prevented from lifting the reward, although they anticipated that food will be lost when moved into the trap. We do not think that the demanding use of an external object is the main reason for the parrots' failure. Moreover, we suppose these parrots fail to consider the trap's position in the beginning of a trial and were not able to stop their behaviour and move the reward in the trap's opposite direction.