The authors of the study show that birds have developed four similar innovations for intelligence during their evolution, independently of mammals.
First, birds have many more nerve cells in their small brains than previously believed. Corvids in particular place this extra portion of computing capacity in those areas of the brain that are most important for cognition.
The second reason is that birds have a specialized brain structure that is similar to the prefrontal cortex in mammals and is crucial for abstraction and planning. This brain region is moreover exceptionally large in intelligent birds and mammals.
Third, birds and mammals alike have a system that uses the neurotransmitter dopamine to constantly feedback the quality of their decisions to the prefrontal system. As a result, the prefrontal computational processes continuously adapt to changing situations and the success or failure of the decisions of the individual.
Finally, birds have independently developed a very similar working memory to temporarily hold things in short-term memory. Like jugglers who constantly keep many balls spinning in the air, birds and mammals use a flexible activity pattern of their nerve cells to keep a lot of information active at the same time.
Critter smarts keep getting more and more street cred.