'Among other things, they are capable of thinking logically, of recognising themselves in the mirror and of empathy.'
The study highlights the fact that birds and apes use different brain structures to think.
Mammals' cognitive skills are controlled by a part of the brain called the neocortex, while crows and parrots manage complex mental tasks with a structure called the pallium.
Professor Onur Gunturkun, of Germany's Ruhr University, and Professor Thomas Bugnyar, of the University of Vienna in Austria, speculate that a common ancestor between apes and birds may have passed on a brain module that is similar in both.
However, they believe a more likely explanation is that they evolved independently of each other by facing the same challenges of survival.
The scientists, whose study is published in the journal Trends in Cognitive Sciences, think this would mean certain brain 'wiring' patterns are necessary to boost cognitive skills.
Professor Gunturkun said: 'What is clear is that the multi-layered mammalian cortex is not required for complex cognition. The absolute brain weight is not relevant for mental abilities, either.'
While ape brains weigh 10oz to just over a pound on average, those of birds weight 0.2-0.7oz.