Bad Luck.

The Fledglings understand more than he said. They understand that they are not to eat at all until the defenses of the pack in the mountain has been breached. They understand that if they allow themselves to be distracted during the process of clearing out the sentries, then they will taught a very painful lesson worse than death. 

Xigger said to them. "Go now."

The five fledglings blurred away from him. They moved at speeds nearing the speed of sound. Their steps are also silent. Each one of them has the strength of Mana entities. The sentries were no match for them. They can kill any guard as easily as snapping the neck of a chicken with a single hand. 

But they didn't go around killing the guards with reckless abandon. They aimed for the Alphas in each squad first and killed them silently. Then they killed the Betas as fast as possible. That is the most effective way to get rid of the sentries without alerting the pack.