 Of those species tested in the delay condition, parrots, rooks, and otters failed.In 2008, Seed, Clayton and Emery said the study of the proximate mechanisms underpinning cooperation in animals was in its infancy, due in part to the poor performances of animals such as chimpanzees in early tests that did not take factors such as inter-individual tolerance into account.In 2006, Melis, Hare, and Tomasello had shown that the performance of chimpanzees in cooperative tasks was strongly influenced by levels of inter-individual tolerance .Several studies since have highlighted the fact that tolerance has a direct impact on cooperation success, as the more tolerant an animal is around food the better it performs.