(Original work by Mr/Mrs/Ms Trad, this version by Shirley Collins). Deconstructing the lyrics suggests that the subject, although with ample cause for regret (death of, or prolonged absence of, spouse) gives way to fits of melancholia only at either high or low tide in May, about a month before the summer solstice. The fact that the birds were singing at the time is probably an artefact which can be discarded for the purposes of this research.
There is a degree of inaccuracy in the data; the tide actually advances by about an hour each day, so the lyrics should read, "Twice point zero four one (rounded) each day returning"