The thrush in "The Hobbit" heard the conversation between the characters. It might have been gathering information to pass on to someone or something else. This information would later play a significant role in the story.
The thrush in the story "The Hobbit" listened to the conversation between the characters. It heard what they were talking about. Since the thrush is a bird, it probably doesn't understand human language like we do. Instead, it might have been listening to the tone of their voices or the general sounds they were making.
When the stars came out, the thrush flew away. Based on this information, we can predict that the thrush might have been gathering information to pass on to someone or something else. In the story, the thrush actually plays an important role by delivering a message to the protagonist, Bilbo Baggins. This suggests that the thrush might have been gathering information to communicate with another character or to fulfill its own role in the story.