111 years ago today, on September 1, 1914 (July 12, 1914 in the lunar calendar), the world's last domesticated passenger pigeon died in the United States. In the early 19th century, billions of passenger pigeons inhabit eastern North America, and migratory birds could block the sky and the sun for days. After that, people migrated westward in large numbers, and millions of passenger pigeons were killed every year. They were also transported by train to cities for sale. The number of passenger pigeons dropped sharply from 1870, when on September 1, 1914, the passenger pigeon was officially designated as an extinct species. A passenger pigeon monument stands in Wyalusing Park, Wisconsin, which reads: "This species was extinct due to human greed and selfishness." In 1900, the last wild passenger pigeon was killed by greedy hunters. The U.S. government once issued a special reward: Anyone who finds a passenger pigeon will receive a reward of US$1500. But no one was rewarded. On the afternoon of September 1, 1914, the last captive female passenger pigeon named Martha died at the Cincinnati Zoo in the United States, which meant that the passenger pigeon had disappeared from the earth.