Julia, I was going to ask you the title of the song you posted, but I found Rickert's Ancient English Christmas Carols: 1400-1700 complet in two locations:

• here (click)
  and
  
• here (click)

The first text looks better than the second, which is raw OCR.

Anyhow, Rickert calls the song, "A blessed bird, as I you say, That died and rose on Good Friday"
-which is quite a mouthful.

-Joe-