use shift + lock to lock at least one flock of birds from laying eggs. Or see if you can destroy those eggs in second turn with some fire spell. Primary thing is to make enemy have less units, not to allow them to have more.
I think that in this case less is really really much more. Try demons or executioners. Buff them up, you can res them later, you can cast divine armor on them. I passed Ziraks 4 times, 2 times on normal, one har and one imposible, he wasn't a problem, but I always had one stack of units (2x BK's, 2x red dragons) lizards are -10% to fire...