Carriers

RFC1149 - A standard for the Transmission of IP Datagrams on Avian Carriers

RFC3043 - IP Encapsulation for Carrier Pigeons

CPIP - Carrier Pigeon IP, the only known implementation of CPIP in existance.

Origination/Dropoff Systems

Carrier Pigeon Roost - Plans by Dave Henderson are archived here. The original lives here.