Originally Posted by Debihuman
This really should be a spell-like ability; it should be a Standard Action; and it should be limited to a number of times per day. A silence spell cast by a 10th level caster lasts 10 minutes so why does the crow need to continue to crow? It doesn't have to maintain the spell. Rather, it should be able to use this ability 2 times per day (since you already based it on Con 14).
It does have to maintain the crow, because it's not casting. It has an ability that 'duplicates' the effects, i.e. the area of silence while it makes a specific action, but does not 'cast'.
I only gave it a 10th level caster level for the purposes of spells that remove silence.