House Wrens usually nest in our yard every year and are regularly heard.
The other day I was working in the yard and I was very puzzled, I heard the wren but his song ended with a very clear, distinct, and lovely "sweet, sweet, sweet." This was repeated numerous times. I got my binoculars and watched him, just to be sure I was hearing him. I was.
Later in the day he returned to his normal "song."
Then late yesterday afternoon his was back to ending with "sweet, sweet, sweet," even uttering a couple of "sweet, sweet, sweet, sweet" without any of his typical call.
Perhaps this is common, but it was new to me.
Clear skies, Alan