Corvids are defined by Wikipedia as "a cosmopolitan family of oscine passerine birds that contains the crows, ravens, rooks, magpies, jackdaws, jays, treepies, choughs, and nutcrackers." They have been shown to be among the smartest birds.
For example, a recent study found that Hooded Crows could memorize the features of paper squares and then create a match by ripping colored paper into similar sizes.
Corvid intelligence has been compared to great apes - animals with much larger brains. Research suggests that while birds and mammals use similar problem-solving mental algorithms, birds independently evolved to use different brain components and nerve connections for these tasks. Another study showed that when using stone tools, more proficient American Crows used different parts of their brains than less proficient individuals.