We are coming up on the 100th anniversary of one of the saddest days in ornithological history. On Sept. 1, 1914, the last remaining passenger pigeon, a female named Martha, died in captivity in the Cincinnati Zoo. A species that had been astoundingly abundant had vanished from Earth.

Passenger pigeons had a large range, spanning eastern Canada south to the Gulf coast and west to western Texas and Montana. They resembled the mourning dove but were much larger, up to 17 inches long. Their feathers glowed with red, gold and blue iridescence. The word “passenger” in their name refers to their migratory tendencies, not to their use in carrying messages for humans.

In the early 19th century, passenger pigeons were more abundant than all other North American birds combined. There is a report of one flock that contained more than 2 billion birds. Audubon reported a migrating flock in Kentucky that blackened the sky for three days. Some nesting colonies were 20 miles across. Such numbers boggle the mind.

In Maine, passenger pigeons were summer residents. They were common enough to provide successful hunting until around 1850. The first record of passenger pigeons in Maine dates from the French explorer Samuel Champlain who found them on islands near Cape Porpoise.

Why did this species go extinct? The answer is probably obvious: humans. A large industry developed in the 19th century to provide passenger pigeon meat for the tables of European immigrants to the United States. Because of the pigeons’ flocking and colonial nesting behavior, they were easy targets. Large numbers could be harvested with ease. Some were caught in nets, others fell to the ground after being smoked with sulfur fires, yet others were killed by guns. Special guns, precursors to machine guns, were developed to allow large numbers of pigeons to be killed quickly.

The harvest of what seemed like an infinite resource was not regulated. The development of railroads, which provided a fast way to get pigeon meat to eastern markets, drove the hunting to an even greater intensity. By the mid-19th century, several thousand people derived a livelihood from harvesting and selling passenger pigeons. One processing plant in New York handled 18,000 birds a day. A billion birds were harvested in a single year in Michigan.

But how could the most abundant bird in North America be harvested to extinction? As the population started to decline, one would expect the industry to collapse, giving the ravaged passenger pigeon population a chance to recover.

The answer appears to lie in the highly social nature of the species. The gonads of most birds regress to a fraction of their active size during the non-breeding season. Changing day lengths cause birds to increase their sex hormones and their gonads enlarge. Rather than increasing day length, the cue for passenger pigeons to enlarge their reproductive organs and initiate nesting was the social stimulation of many passenger pigeons in a local area. Without a large enough concentration of birds, the reproductive cycle did not begin.

The collapse of the passenger pigeon started around 1880 and commercial hunting, no longer profitable, ceased. Unfortunately, the large flocks of passenger pigeons were dispersed across the continent in smaller groups. These flocks may never have gotten large enough to induce the start of the nesting cycle.

The population continued to decline and was extinct in the wild until 1900. The last passenger pigeon reported in Maine was shot in Dexter in 1896. Efforts to breed them in captivity failed. Martha was the last of her species, gone 100 years ago.

Herb Wilson teaches ornithology and other biology courses at Colby College. He welcomes reader questions and comments at

whwilson@colby.edu