Passenger Pigeon - Behavior and Ecology

Behavior and Ecology

The Passenger Pigeon was a very social bird. It lived in colonies stretching over hundreds of square miles, practicing communal breeding with up to a hundred nests in a single tree. It may have been the most numerous bird on earth in its heyday, and A. W. Schorger believed it accounted for between 25 and 40% of the total landbird population in the US. Pigeon migration, in flocks numbering billions, was a spectacle without parallel, as described by John James Audubon:

I dismounted, seated myself on an eminence, and began to mark with my pencil, making a dot for every flock that passed. In a short time finding the task which I had, undertaken impracticable, as the birds poured in in countless multitudes, I rose, and counting the dots then put down, found that 163 had been made in twenty-one minutes. I traveled on, and still met more the farther I proceeded. The air was literally filled with Pigeons; the light of noon-day was obscured as by an eclipse, the dung fell in spots, not unlike melting flakes of snow; and the continued buzz of wings had a tendency to lull my senses to repose... Before sunset I reached Louisville, distance from Hardensburgh fifty-five miles. The Pigeons were still passing in undiminished numbers, and continued to do so for three days in succession.

Their survival was thought to be based on the benefits of very large numbers. There was safety in large flocks, which often numbered hundreds of thousands of birds. When a flock of this huge size established itself in an area, the number of local animal predators (such as wolves, foxes, weasels, and hawks) was so small compared to the total number of birds, little damage would be inflicted on the flock as a whole. It was common for birds in flocks to perch on each other's backs, an unusual behavior even for socially inclined birds.

The bird is believed to have played a large ecological role in the presettlement forests of North America through tree breakage and depositing of excrement, thereby influencing the distribution of certain tree types.