Lesson
White to move. Main line: 1. Qf4#
From f4 the queen checks the king diagonally on e5 and controls d4, e4, f5, f6 and d6. The white king on g4 protects the queen, so Black cannot capture the checking piece.
The queen does not control d5 or e6 from f4—but Black’s own pawns already occupy those squares. Those two self-blockers complete the mate and make the position resemble a bird’s spread tail, giving the pattern its name.
When an enemy king is surrounded by its own pieces, map the few squares your queen does not cover. A contact check becomes mate when friendly protection secures the queen and the defender’s army supplies the remaining walls.