Before the 1900s, passenger pigeons made up about 40 percent of the total bird population in the US. These birds migrated in massive colonies, and there were so many of them that they could actually black out the sun. Passenger pigeons were over-hunted primarily because their nesting habits made them an easy target. Hunters in North America wouldn’t have believed that the species was in danger of becoming extinct. A single tree could house over 100 nests. This also made it easy for infectious diseases to spread through the colonies. By the late nineteenth century it was rare to come across a passenger pigeon. Some attempts were made to save the passenger pigeon from extinction, but it was too late. The last remaining passenger pigeon was named “Martha” after George Washington’s wife. Her preserved remains are in the Smithsonian collection.