It seems like our misestimation of animal intelligence always goes in this direction. Have we discovered recently that any species are less smart than we'd thought? (besides humans, yuk yuk)
Unlikely as most researchers operate from the point of view that all animals are mindless automatons acting from pure instinct until proven beyond a doubt. Even then they will warn you against the heady Dangers of Anthropomorphizing Animals and Projecting your Emotions onto Unthinking and Unfeeling Lumps of Meat.
There are numerous discoveries of the limits of animal intelligence, especially in the area of language acquisition. Especially when Skinner's behaviorism concept was in vogue, it had actually been assumed that at least some animals could learn human-like language with enough training. This turned out to be completely false even for animals like chimpanzees and gorillas. In fact, some of the exact limits were identified - especially around syntax and embedding (one phrase inside another).
You can read up on a chimpanzee called Nim Chimpsky to see one of the more infamous failures in this area (and quite a sad story of animal mistreatment). It also illustrates the dangers of wanting to believe, or of excessive anthropomorphizing - as initially the experiments were deemed successful, until more dispassionate analysis showed that the chimp's signing was far more random and determined than presented.
I assumed chickens would have been much smarter than they turned out to be when we got some. Birds are known to be smart, just not all birds as it turns out.
Pheasants are as dumb as boxes of rocks. Their road sense is awful, and generally do exactly the wrong thing at exactly the wrong time.
In the dim and distant past I worked as a programmer at a company that bought an old country estate for one of its offices. As part of the estate there were about a dozen peacocks. There were none left when I joined though. My manager explained that they were completely dumb and kept get run over.