Blue-throated macaws (Ara glaucogularis) succeed in a cooperative task without coordinating their actions

Social complexity may select for socio-cognitive abilities. The loose string task has become a comparative benchmark paradigm for investigating cooperative problem-solving abilities in many species, thus enhancing our understanding of their evolution. It requires two individuals working together to solve a problem, specifically by pulling the two ends of a string simultaneously to move a reward towards them. A dyad's performance therefore depends on the individuals' ability to coordinate their pulling action. Many species, including corvids and parrots, have been tested in this paradigm, but most appear insensitive to the exact cooperative nature of the task. We tested another parrot species, blue-throated macaws, to further our understanding of social cognition in psittacids. Five birds were tested with different partners in a dyadic setting. The study included two control conditions examining the cognitive mechanism underlying their seemingly cooperative behaviour. All birds were able to simultaneously pull the strings, but their performance did not drop when they were denied mutual visual access, and they failed to obtain food when they needed to wait for their partner. Moreover, the parrots decreased their latency to pull with increasing experience. These findings suggest that the birds may have applied an associatively learnt rule, or relied on acoustic cues, rather than coordinating their actions with the partner. This may not necessarily prove a lack of understanding the partner's role, given that their failure to wait in the delay control test might be explained by their poor inhibitory control abilities. Relationship quality (i.e. affiliation and food tolerance) did not influence dyadic success. Future studies are needed in order to disentangle macaws' potentially limited cooperative abilities from their lack of inhibitory control.