Every time I read an article to the effect that researchers have discovered that some non-human creature has a capability previously believed to be unique to humans, I ask myself (and usually those around me) if these researchers have ever had a dog or cat, or closely watched squirrels, crows, goats, or any of a hundred other animal species. There is so much evidence of nonhuman sentience right there in front of us that it very nearly takes a conscious effort not to see it.
I wouldn't call squirrels intellectual giants, but if you assume sentience in, say, every vertebrate unless there's evidence to the contrary, you'll be right more often than not. Of course, this raises an interesting ethical dilemma for those of us who are omnivores, but pretending it isn't there doesn't make it go away. (For my part, I consider this is an argument for humane livestock practices.)