I bet you the bird IS the Rook attack but it's sent by the Rook, like Elphaba's flying monkeys or Selina Kyle's cats. I bet the Rook is a lot more like Dr. Claw from Inspector Gadget!
In chess terms, a rook is the castle shaped piece, not the most important piece. Wonder if there's a king or queen behind the shadows controlling the rook (as "pawns").
The "Rook" is really a Glitch, that was driven from Ur centuries ago, for being a Black Magician. He found the Rooks in the baren wasteland that he inhabits, enslaved them and took on the name "Rook". For centuries, he has been plotting his attack - his revenge. And now, the time has come. He's starting with small attacks on individual streets, but that's only the beginning. It's going to get much, much worse. Soon, he'll start attacking countries - Groddle Meadow, Jethimadh, Groddle Forest, etc. Eventually, once we're weakened, he'll start a full-scale attack on the whole of Ur. We must stop him before he is too strong.