You might joke about sending a friend something via carrier pigeon, but the Pigeon Post program actually allows you to do so. Disappointingly, the bird itself has been manufactured in plastic, but this does eliminate the possibility of inflicting animal cruelty.
See, what you're doing is shoving your hollow bird into a regular neighborhood mailbox -- and it genuinely fits! Letter Writers Alliance provides you with mailing label pouches, message forms, some postage stamps and dispatching instructions. Over time, its feathers might suffer from a few scuffs, but you can carry on interstate correspondence with a friend for quite a while with your durable urban bird courier.
There are a few things that you might like to know about Pigeon Post: letters sent must be American domestic, and yes, the United States Postal Service will deliver your plumed package to its destination.