Recently, MacLean et al. (MacLean et al. 2014 ) conducted a large-scale study involving 36 species, comparing motor self-regulation across taxa - concluding that absolute brain size predicts level of performance. The great apes were most successful, and only a few of the species tested were birds. Given birds' small brain size—in absolute terms—yet flexible behaviour, their motor self-regulation called for closer study.
As corvids exhibit some of the largest relative avian brain sizes—although small in absolute measure—as well as the most flexible cognition in the animal kingdom, we therefore tested ravens, New Caledonian crows and jackdaws in the so-called cylinder task.
The results showed that the performance of the crow birds was indistinguishable from that of great apes despite the much smaller brains, and that both absolute and relative brain volume to be a reliable predictor of performance within Aves.