[orthodonticjake]

I see no rule that says an adult cannot be mailed

[charcircuit]

>Domestic packages may not weigh more than 70 pounds.

https://faq.usps.com/articles/Knowledge/Parcel-Size-Weight-F...

Adults are too heavy.

[LorenDB]

That has been done as well.

https://en.wikipedia.org/wiki/Henry_Box_Brown

[tolerance]

This TIL struck like a laxative!

[lxgr]

Adult birds can explicitly be mailed: https://pe.usps.com/text/pub52/pub52c5_008.htm

[MikeTheGreat]

It's weirdly hilarious that they allow day-old birds, and adult birds, but apparently nothing in between.

So you can order chicks by mail, but you can't return them by mail (unless birth + packaging + USPS shipping, including delivery + return packaging + delivering return package to USPS for return mailing all takes < 24 hours, total, I guess)

[shawn_w]

Every spring, chicken hatcheries mail out newborn chicks en masse. I've gone to my post office and heard chirping coming from the back many a time.

Babies wouldn't be much different. Just need bigger air holes in the box.