I've never really seen a satisfactory definition of what intelligence is. Descriptions of intelligence have seemed a little vague. The thought occurred to me a while back, and I've no idea that it's right, that maybe the only objective, observable measurement of intelligence might lie in a being's capacity to invent technology, to manipulate the natural universe by artificial means, essentially, to use tools. For example, a bird that uses grass and leaves to build its nest might be considered to be engaging in an act of intelligence, because it's rearranging the universe to its advantage. Or an ape that grasps a twig and inserts it into an ant-hole, so it can extract the ants, without having to paw into the dirt.
I'm not sure that behavior (the successful attainment of a goal) is necessarily a valid way to assess intelligence. The tube test cited in the study seems to be based on visual acuity alone. It doesn't take into consideration that, while the tube is transparent, it effectively blocks the smell of the food. How do we know the animal isn't just following its nose to the food?
Where do we draw the line between what is instinctual and what is intelligent? Any thoughts?