Live animals is the grenade in the game of paper/rock/scissors - it beats them all. If a cop can violate your fourth amendment rights by breaking into your car to free an overheated dog, there should be no quarrel about opening a box containing chicks to render life saving aid.
They can go 4 days without food or water. If they're stuck beyond that in an office far away, I get it, and some post offices even offer stuck chicks for free to anyone who will come take them, which is awesome and I fully support that. But if I get an opened box of chicks after they've been only four days in transit, I am raising hell.