Interspecies coevolution of languages on the Northwest Coast.
During the years I spent kayaking along the coast of British Columbia and Southeast Alaska, I observed that the local raven populations spoke in distinct dialects, corresponding surprisingly closely to the geographic divisions between the indigenous human language groups. Ravens from Kwakiutl, Tsimshian, Haida, or Tlingit territory sounded different, especially in their characteristic "tok" and "tlik."
I believe this correspondence between human language and raven language is more than coincidence, though this would be difficult to prove.