The morning found me reading John James Audubon's The Passenger Pigeon. My appetite was whet. Audubon had no idea that the great numbers of Passenger Pigeons he was writing and drawing about, would some day become extinct. Audubon was writing in 1813.
One 1855 account from Columbus, Ohio, described a “growing cloud” that blotted out the sun as it advanced toward the city. “Children screamed and ran for home,” it said. “Women gathered their long skirts and hurried for the shelter of stores. Horses bolted. A few people mumbled frightened words about the approach of the millennium, and several dropped on their knees and prayed.” When the flock had passed over, two hours later, “the town looked ghostly in the now-bright sunlight that illuminated a world plated with pigeon ejecta.” http://www.audubon.org/magazine/may-june-2014/why-passenger-pigeon-went-extinct
It seems that their survival depended upon their flocking behaviors. They had to stick together. However, their demise is still debated as to whether they died from some sort of avian disease or were over hunted. Usually, it's "both and and."
What a phenomena!