Dalemen:

The Men of Dale, both before its destruction by the dragon Smaug and after it was rebuilt. There was one peculiarity to the Dalemen, they could understand the speech of thrushes. It was by this method that the weakness of Smaug was told to Bard.
The Men of Dale used to have the trick of understanding their language, and used them for messengers to fly to the Men of the Lake and elsewhere. (H.217)

After the rebuilding of Dale, Bard became its first king.