To whom did an angel announce Jesus' birth in the fields at night?

Answer: Shepherds

An angel of the Lord appeared to shepherds keeping watch over their flocks by night, and the glory of the Lord shone around them.

“And there were shepherds residing in the fields nearby, keeping watch over their flocks by night. Just then an angel of the Lord stood before them, and the glory of the Lord shone around them, and they were terrified.”— Luke 2:8-9 (BSB)