Delancey Place posted a fascinating excerpt on carrier pigeons from Saladin by John Man.
The historian al-Maqrizi recorded one very non-routine use of homing pigeons. In the late tenth century, the fifth Fatimid caliph al-Aziz loved the cherries of Baalbek. As a treat, his vizier -- in effect, prime minister -- arranged for 600 homing pigeons to be sent off from Baalbek to Cairo, each carrying a silk bag attached to either leg, with a single cherry inside each bag. The pigeons had 600 kilometres to fly. If they left in the morning, al-Aziz could have had fresh cherries for dessert that evening, with enough left over for his many guests.