Crow searching for a nut I'd hidden and then making very cool woo sound

One day on the beach, I heard a crow make a sound I hadn't heard before. So I gave him/her a nut. Little by little the crow started to come around as soon as I arrived on the beach and figuring out that nuts are associated with the woo sound, now makes them regularly. I've also been teaching her/him to search under an empty oyster shell for a nut I've hidden there. Little by little I've stacked more shells and rocks over the hidden nut. Pretty smart bird.