According to USPS shipping regulations, the birds must be shipped without food or water. So technically, all of these suggestions are illegal. That being said, many who ship include something solid that won't melt or get gooey, like apple slices or cucumbers. Remember that the boxes are dark and the birds will be mostly sleeping during their trip.
Disease-free adult fowl may be mailed domestically when shipped under applicable law in accordance with DMM 601.1.7. Adult chickens, turkeys, guinea fowl, doves, pigeons, pheasants, partridges, quail, ducks, geese, and swans are mailable when properly packaged. Adult fowl must be packaged without food or water because liquids, moisture, and loose foodstuffs can cause damage to the shipping container, other mail, and Postal Service equipment during transport.
Rosalyn
Rosalyn