Cockatoos are not the only ones
I've seen a Macaw show even more intelligence. At my engineering college some kind people donated him as a leaving present and he lived in the students' bar, kept on his perch by a long very light chain attached by a ring with a split thread to his leg. Initially the ring was fastened with a simple nut. He got it off within 2 days. So we made another with a left handed thread. 2 days later he was out. So we fitted a lock nut. It took him a week to figure out that by using his own weight on his feeding bowl he could hold one nut whilst undoing the other. After that we gave up and he had the run of the bar, until he swore once too many times in front of the ladies and was sent off to the zoo. Unfortunately, because of his language he could not go on public display and was confined to a back area where he was eventually murdered by a badger.