Why is this a tie?

sclukey


Ok, so this is a very old game, but from the initial position, can anyone see why Bird agreed to a tie when he clearly had a mate in 3? Please, if you see ANY reason why feel free to contradict me. I mean, I'm not exactly a chess genius and I saw that mate...
rooperi

2 Rb6????? No, 2 Rf7+, followed by RxN

[EDIT] After this, White will win, Black has to play 1 Kg8, and and Whote has to continue checking, the Black King can never go to the f file

idosheepallnight

The black king has to move forever to h8 g8 and g7. If it dares move to the f file black loses the N and the game.

sclukey

Ok...I knew I should be missing something. Thanx you guys.