Currently, birb can be easily countered using the dragon's roar. Here's what I think should get changed:
Birb should be imune to being scared (entering "balloon" mode) mid-flight after being thrown by a crusader.
After being scared, a crusader carrying birb should automatically throw it in the direction he was looking in.
After hitting something (the dragon, a wall, the floor) after either of the previously mentioned events (birb being scared mid-flight or birb getting thrown due to the crusader carrying it getting scared), birb should enter "balloon" mode automatically.
These three changes would make birb much more useful at the role it's supposed to fill- punishing camping dragons, as a simple roar would no longer completely negate its function. The dragon would have to actually dodge it or get hit.