The Thrush seems communicates to some but not all. Which birds can talk to which types of creatures, in The Hobbit?
Three types of birds feature prominently in The Hobbit: Eagles, thrushes, and ravens, and all three of these birds can to some extent communicate with the other races of creatures, like men or dwarves.
The Great Eagles who rescue the dwarves, Gandalf, and Bilbo from the goblins in the Misty Mountains have the ability to speak and communicate. The Lord of the Eagles mostly speaks to Gandalf, but Bilbo and the dwarves can all understand him.
The thrushes could communicate with the Men of Dale who "had a trick of understanding their language, and used them for messengers" (205). When Bard, the captain of the archers, prepares to defend the Lake Town against Smaug, the old thrush from the Lonely Mountain warned him that the dragon had a weak spot under his left breast.
Balin hears the thrush but cannot understand him, telling Bilbo:
"I cannot follow the speech of such birds, it is very quick and difficult [...] I only wish he were a raven!" (230).
Having heard the dwarf say this, the thrush flies away and returns with the son of the old raven Carc who used to live near the Lonely Mountain. The ravens, an ancient breed, according to Balin, often acted as messengers and bearers of secret news. Unlike crows, the ravens were intelligent and quick witted. Carc's son, Roac, brings news to the dwarves that Smaug is dead, but many wish to lay claim to Thror's treasure.