72–76One animal which has become extinct was once probably the most numerous bird in North America: the passenger pigeon. The passenger pigeon bred in the eastern part of the U.S. and Canada and often migrated to the southern U.S. during the winter months. The bird’s name came not from the migrations but from its highly visible movements in search of food. The passenger pigeons were social birds, traveling in amazingly large numbers that ranged from the millions to one or two billion. Passing overhead on a broad front, a flock of birds could darken the sky as effectively as storm clouds for a period of hours.Passenger pigeons bred in huge colonies, and these colonies frequently covered many square miles. A hundred or more pairs of pigeons often nested in the same tree, each female laying a single egg. The birds lived mainly on wild seeds and nuts, but sometimes a flock would swoop down onto a field or a garden and eat everything in sight.While vast numbers of passenger pigeons were recorded in the late nineteenth century, the population declined rapidly, and the last wild bird was shot in 1904. The swift disappearance of the bird remains a mystery, but a partial explanation is found in its habit of nesting and moving in a large flock. Farmers, who considered them pests, found it easy to catch hundreds at a time in nets. Also, as passenger pigeons were tasty game birds, market hunters shot hundreds of thousands on their nesting grounds. By 1900 the passenger pigeon was already rare.
72. What is the main subject of this article?
(A) The history of the passenger pigeon
(B) The life cycle of a passenger pigeon
(C) The migration habits of passenger pigeons
(D) The large market for passenger pigeons