The real carrier pigeon is a large bird with long wings, a large tuberculated mass of naked skin at the base of the beak, and a circle of naked skin round the eyes, but the variety generally employed to carry messages more resembles an ordinary pigeon.

The practice of sending letters by pigeons belongs originally to Eastern countries, though in other countries it has often been adopted, more especially before the invention of the electric telegraph. An actual post-system in which pigeons were the messengers was established at Bagdad by the Sultan Nureddin Mahmud, who died in 1174, and lasted till 1258, when Bagdad fell into the hands of the Mongols and was destroyed by them.

These birds can be utilized in this way only in virtue of what is called their "homing" faculty or instinct, which enables them to find their way back home from surprising distances. But if they are taken to the place from which the message is to be sent and kept there too long, say over a fortnight, they will forget their home and not return to it. They are tried first with short distances, which are then gradually increased. The missive may be fastened to the wing or the tail, and must be quite small and attached so as not to interfere with the bird's flight.

By the use of microphotography a long message may be conveyed in this way, and such were received by the besieged residents in Paris during the Franco-Prussian War of 1870-71 the birds being conveyed out of the city in balloons.

Seventy-two miles in two and one-half hours, a hundred and eighty in four and one-half, have been accomplished by carrier pigeons. Large numbers of these birds are now kept in England, Belgium, France, etc., there being numerous pigeon clubs which hold pigeon races to test the speed of the birds. These pigeons are also kept in several European countries for military purposes.