Not only that, USPS is the only "major" carrier who will do so.

Yeah they are quite hardy. Have ordered on 2 seperate occasions, all arrive healthy. When a chick is born they essentially consume the yolk which will allow them to go a couple days without needing food/water. Being a live shipment you usually pick it up at the post office, so it doesn't have to get trucked around all day. (Also meaning you can grab them as soon as they are supposed to be there and get them all settled in under a heat source and food/water quickly).

And boxes of spiders.

And bees, and crickets. Different boxes tho

I read your comment before the one you replied to and my mind certainly went somewhere other then farms

While it may seem kind of weird I’ve raised about 100 chickens that came via the mail.

I haven’t lost any of these and they all lived a great life outside on the farm.

You can but they may arrive slightly squishy.

The post office changed their provider for air mail a few years ago and they don’t seem to want to give priority to living things and frequently stack heavy items on top of live stock boxes…

Most farms try to source them locally now to avoid killing hundreds of chicks while in transit.