During the Franco-Prussian War, which lasted from 1870–1871, Paris was under complete siege and all regular communications were cut off from the rest of France. This complete halting of communications was due to the efficiency of the Prussians, who moved into Paris only six weeks after the war began. As in any wartime situation where communications are disrupted, there is always an attempt to get them back; postmen continued to try to carry messages in and out of Paris, but they were usually captured and sometimes shot. Another attempt by the citizens of Paris was to send sheepdogs out of the city by way of balloons, with the hope that they would carry a message back to the city from the outside. They were never seen again.
By this point the besieged Parisians turned to the only option they had left: carrier pigeons. On the inception of this idea to use carrier pigeons to transport messages, 1000 pigeons were moved into the city. There was, of course, time spent and mistakes made, but on September 27, 1870, the first pigeon flew out of Paris carrying a secret message. On October 1, the pigeon returned.
While this method of communication did turn out to be successful, it was by no means a certainty. Natural predators, hunters, and the general dangers of wartime conditions made this a very dangerous job for the pigeons, and some never returned. But during the course of the war, the carrier pigeons delivered several official dispatches and over 95,000 private messages.
At first the messages were written on thin pieces of paper, tightly rolled, and attached with a piece of thread to one of the tail feathers. Later, a photographer in Paris named Dagron developed a form of microphotography to be used to shrink the written messages even further, and more detailed communiqu s were then possible.
By the war's end in 1871, other European powers had taken notice of this form of communication and set up their own "pigeon sections" within their armies. It was only when wireless communications became common that the need for carrier pigeons became obsolete.