So when you hold an action using the Ready action you use your reaction to act when the trigger happens. however you're able to ignore the trigger. So while you are using the Ready action, are you able to take a DIFFERENT reaction before the trigger (or after if you ignored it) at the cost of losing the readied action?
Scenario: Fighter is fighting a bird and a goblin. The goblin is in melee range. The fighter readies a sword attack for when the bird comes into range. The goblin acts before the bird and leaves the fighter's range. Can the Fighter take an attack of opportunity - expending his reaction, and thus unreadying the attack on the bird?