Biologists can get a bit flustered when they hear the slur "bird brain," meant to insult a person's intelligence. Birds are capable of doing amazing things, like using tools or making nests that withstand water. Yet, because birds have evolved on a different track than those of mammals and particularly humans, birds have gotten the short end of the stick. However, a recent study conducted may give birds the respect for their intelligence that they deserve.

Conducted on grey parrots, Christian Schloegel and his colleagues in Austria and Germany performed an experiment that had heretofore only been conducted with primates. They had two boxes, one containing walnuts, and one tjat was empty. They would rattle both boxes, giving the indication of food. When this experiment had been conducted with apes, apes would seek out the rattling boxes but remain in place when they heard the empty boxes, recognizing that there was no food in them.

When the experiment was recreated with parrots – marking this as the first time that the experiment had been conducted with birds – the six grey parrots performed the same as apes. Just like apes, they inferred that a noisy box was a full one, and similarly inferred that a silent box was an empty box.

While this ability may not seem that impressive, it is something that humans cannot master until the first three years of their lives. In addition, aside from apes, no other animal was shown to be able to do this, not even monkeys or dogs.

Interestingly though, parrots were better at observing the acoustic cues when boxes were shaken horizontally rather than vertically. Researchers noted that vertical shaking resembled parrots' head-bobbing, so it may have confused them.

Parrot – or psychology – devotees will note that parrots have already proven themselves to be pretty intelligent. The late Alex the parrot, who died in 2007 after 30 years of experiments, was able to count up to 8, and could add two objects together as long as the total did not exceed 6, meaning that his mathematical skills were on par with or exceeded the skills of chimpanzees and other non-human primates. (And let's face it: some humans.) Parrots are also able to speak, and even though their conversation is really just mimicry, that capacity far outpaces that of other birds.

The study was published in the journal, Proceedings of the Royal Society.