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)
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.
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.