I am indebted to Mr. William Kelly of Leicester for the following note on the Leicestershire superstition of the Seven Whistlers.
"There is an old superstition, which it is not easy to get to the bottom of, concerning a certain cry or sound heard in the night, supposed to be produced by the Seven Whistlers. What or who those whistlers are is an unsolved problem. In some districts they are popularly believed to be witches, in others ghosts, in others devils, while in the Midland Counties they are supposed to be birds, either plovers or martins—some say swifts. In Leicestershire it is deemed a bad omen to hear the Seven Whistlers, and our old writers supply many passages illustrative of the popular credulity. Spenser, in his Faërie Queene, book II. canto xii. stanza 36, speaks of
The whistler shrill, that whoso hears doth die.
Sir Walter Scott, in The Lady of the Lake, names the bird with which his character associated the cry—
And in the plover's shrilly strain
The signal whistlers heard again.
"When the colliers of Leicestershire are flush of money, we are told, and indulge in a drinking bout, they sometimes hear the warning voice of the Seven Whistlers, get sobered and frightened, and will not descend the pit again till next day. Wordsworth speaks of a countryman who
... the seven birds hath seen, that never part,
Seen the Seven Whistlers in their nightly rounds,
And counted them.
"A few years ago, during a thunderstorm which passed over Leicestershire, and while vivid lightning was darting through the sky, immense flocks of birds were seen flying about, uttering doleful, affrighted cries as they passed, and keeping up for a long time a continual whistling like that made by some kinds of sea-birds. The number must have been immense, for the local newspapers mentioned the same phenomenon in different parts of the neighbouring counties of Northampton, Leicester, and Lincoln. A gentleman, conversing with a countryman on the following day, asked him what kind of birds he supposed them to have been. The man answered, 'They are what we call the Seven Whistlers,' and added that 'whenever they are heard it is considered a sign of some great calamity, and that the last time he had heard them was on the night before the deplorable explosion of fire damp at the Hartley Colliery.'"
In Notes and Queries there are several allusions to this local superstition. In the Fifth Series (vol. ii. p. 264), Oct. 3, 1874, the editor gives a summary of several notes on the subject in vol. viii. of the Fourth Series (pp. 68, 134, 196, and 268), with additional information. He says "record was made of their having been heard in Leicestershire; and that the develin or martin, the swift, and the plover were probably of the whistling fraternity that frightened men. At p. 134 it was shown that Wordsworth had spoken of one who
... the seven birds hath seen, that never part,
Seen the Seven Whistlers in their nightly rounds,
And counted them.