More info i found on the net , why we no longer have the passenger pigeon.
One reason why the passenger pigeon existed in such prodigious numbers was the lack of natural predators apart from hawks and eagles. It was, however, surprisingly vulnerable to human intervention. Each female laid only one egg a year, which made it difficult to replace any losses quickly. Only a flimsy nest was made and its habit of nesting in vast colonies and migrating in huge flocks made it very easy to attack. The birds fed mainly on acorns, chestnuts and beech nuts in the extensive woodlands of North America and so when these were steadily cut down their habitat and food supplies were reduced. Human intervention was at first relatively restrained, largely because of the limited numbers living in North America. The Indians captured the pigeons in large nets and by the 1630s the settlers of New England were doing the same. The young squabs were regarded as a great delicacy and the adults were sought after for their feathers as well as their meat. In the first couple of centuries of European settlement it is doubtful whether the number of pigeons declined very much given the relatively small number of humans in the area. After 1830 the practice of releasing live pigeons from traps for shooting practice began, but this in itself would not have proved fatal to the existence of the species even though about 250,000 a year were being killed in this way in the 1870s.
The population had certainly been reduced by the middle of the nineteenth century but was still several billion strong. The real onslaught began with the onset of large-scale commercial hunting carried out by well-organised trappers and shippers in order to supply the developing cities on the east coast of the United States with a cheap source of meat. It began once railways linking the Great Lakes area with New York opened in the early 1850s. By 1855 300,000 pigeons a year were being sent to New York alone. The worst of the mass slaughter took place in the 1800s and 1870s. The scale of the operation can be judged by figures that seem almost incredible but which were carefully recorded as part of a perfectly legal and highly profitable commerce. On just one day in 1860 (23 July) 235,200 birds were sent east from Grand Rapids in Michigan. During 1874 Oceana County in Michigan sent over 1,000,000 birds to the markets in the east and two years later was sending 400,000 a week at the height of the season and a total of 1,600,000 in the year. In 1869, Van Buren County, also in Michigan, sent 7,500,000 birds to the east. Even in 1880, when numbers had already been severely reduced, 527,000 birds were shipped east from Michigan.
Not surprisingly, even the vast flocks of pigeons could not withstand slaughter on this scale. Numbers fell rapidly and by the late 1880s large flocks, which had once been so common, had become a matter for comment and investigation, and most were no more than a few hundred strong. The last known specimens were seen in most states of the eastern United States, in the 1890s, and the passenger pigeon died out in the wild in Ohio about 1900. The last survivor of a species that had once numbered 5 billion died in captivity in 1914.
