ABSTRACT
Determining what constitutes avian intelligence, much less what selection pressures might have shaped the cognitive architecture that underlies intelligent behavior, is a daunting task. Even after two decades of examining the cognitive and communicative abilities of Grey parrots (Psittacus erithacus) and of following colleagues' studies of the capacities of other avian species, I have more questions than answers. Given these many questions, however, five interrelated ones, three general and two specific to birds, appear particularly relevant to discussions of nonhuman intelligence: First, what actually is intelligence? Second, can we judge nonhuman capacities using human tasks and definitions? Third, how do we fairly test creatures with different sensory systems from ours? Fourth, how does a nonmammalian brain process information? Fifth, to what extent do avian cognitive capacities match those of mammals? Ongoing studies provide only preliminary answers to the first four questions, but considerable data exist to respond to the fifth. To summarize the state of our knowledge, I examine concepts of intelligence and different types or specializations of intelligence, and I review the history of avian cognitive research and studies that indicate advanced cognition, with an emphasis on Grey parrots. I then present some ideas concerning the evolution of intelligence in parrots and possibly other birds.
