February is awful early to be shipping 40 odd baby chicks via a common carrier.
If the size of the biddies were a problem then no one could order, hatch, or raise quail, pheasant's, bantam chicks, etc.
Unless they have constant human supervision and a heat source 24-7, a 40 degree drop in temperature in only 12 hours while in transit will set most biddies so far back that they are unlikely to ever recover.
I know of one commercial hatchery near me (Ross Breeders) who I am told ships 250,000 or more day old chicks at a time for long distances, and at any time of the year to boot. They do this feat in
dedicated trucks that only costs $400,000 each. They, or I should say that their "baby chicks" suffer minimum mortality.
It is not my intent to ridicule USPS employees, but I do think that the latest increase in postage was used to pay for the cost of storing our mail until the USPS delivers it.