From Pieter Folkens:

Re: Rock-throwing zoo chimp stocked ammo in advance: study (March 10): It should be noted that similar behavior (that is, spontaneous plans for future events) has been documented in dolphins for a couple of decades now.

There was a dolphin at Marine World/Africa USA in the 70s and 80s who was trained to retrieve trash from the tank and received a food reward. On many occasions a trainer would come up on deck to a clean tank, completely devoid of trash, and a dolphin with a bit of trash in its mouth asking for the reward. Monthly food review showed that this dolphin was being feed more than the rest. An observer was put below at a viewing port to see if something unusual was going on.

It turned out that this dolphin had a stash of trash in a container lodged in a corner of the pool full of trash. Whenever a trainer came to the deck, the dolphin dutifully went to the stash and took a bit to present to the trainer. It was also noted that the dolphin would reduce large trash items into smaller bits for the stash to last longer.

This dolphin was the first unambiguous evidence that an animal other than primates can make spontaneous plans for future events.

Pieter Folkens
Alaska Whale Foundation/Society for Marine Mammalogy