> ...the crows still had to figure out the center-embedded order where open and closed brackets were paired from the outside in...if the birds only learned that

> ...the crows still had to figure out the center-embedded order where open and closed brackets were paired from the outside in...if the birds only learned that open brackets were at the beginning of the sequence and closed ones were at the end, you would expect an equal proportion of ( { ) } mismatched and correct responses. But...the crows chose more of the latter than the former, even with the more complex sequences of three pairs of brackets. I'm no expert but it seems like the birds are identifying visual symmetry. Maybe they are remembering the mid-point of nested symmetrical symbols, and that's still interesting, but is that "understanding recursion"? Recursion is the idea of repeating an algorithm or a function calling itself. Visual symmetry is a little simpler than that. If a crow peels an onion layer by layer that doesn't mean it understands recursion. It's doing something recursive. Understanding recursion, in my mind, involves being able to describe a recursive function or make a prediction based on understanding the function.