Thursday, December 09, 2010

Retelling tales of the famously extinct passenger pigeon

Retelling tales of the famously extinct passenger pigeon

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[Author's note: this post is a follow up to "The case of the louse and the passenger pigeon" from November 18, 2010.]

For me, the retelling of stories about passenger pigeons, which were extinguished as a species after having been one the most abundant birds on Earth, is like the rehearsal of tales about a loved one at a memorial service: necessary, pleasurable and painful at the same time.

By all accounts individual passenger pigeons were striking birds. Males, which were slightly larger and more colorful than females, measured about 16 inches from beak to tail tip. They were blue-gray on the back, with scattered black markings and iridescent neck feathers that could flash pink, violet, gold and metallic green. Underneath, their throats and chests were colored with mixed shades of orange, red and tan, which faded to dull white on their bellies. An orange-red iris gave their eyes an arresting quality. [Illustration depicting female, above, and male, below, is plate by John J. Audubon.]

But passenger pigeons were even more remarkable en masse. They occurred in hard-to-comprehend numbers; somewhere between three and five billion are estimated to have lived in eastern and central North America when Europeans first arrived here. According to Arlie W. Schorger, who wrote the definitive book on them, passenger pigeons once constituted one-fourth of all birds on the continent.

Passenger pigeons flocked in staggering numbers, too. In an often cited passage from his pioneering work, American Ornithology, Alexander Wilson described a flight near Frankfort, Kentucky in 1806 in these terms: “from right to left as far as the eye could reach, the breadth of this vast procession extended; seemingly everywhere equally crowded.” He estimated the column of birds flying over to be at least a mile wide and, since it passed by at nearly 60mph for more than four hours, a stunning 240 miles long. By Wilson’s calculation the flock would have included nearly two and a quarter billion birds.

Passenger pigeon flocks could be so dense they eclipsed the sun as they passed, and the roar of their wings was likened to thunder, or the approach of a tornado.

In fall, winter, and spring, passenger pigeons fed on the nuts of forest trees, known collectively as mast: primarily beechnuts, acorns and chestnuts. The movement of a feeding flock of passenger pigeons across the ground was like a rolling wave, with the birds at the rear continually flying up and over to take a place along the front of the line.

Mast-producing trees overcome the problem of having their seeds eaten up by producing a superabundance of them at intervals, so there are leftovers to sprout even after consumers have had their fill. The survival strategy of passenger pigeons was similar; individuals were, in many circumstances, easy prey. But flocks were so large that local predators could be sated without diminishing passenger pigeon populations over time.

Passenger pigeons nested in enormous colonies, which were often be measured in square miles. The largest nesting ever recorded, which took place in central Wisconsin in 1871, occupied most of the southern two-thirds of the state.
Scientists still contend over the relative importance of factors that caused the extinction of passenger pigeons. But at the top of the list are market hunting, which intensified to shocking degrees after the mid-nineteenth century, and the wholesale destruction of the eastern forest.

The pain in contemplating passenger pigeons comes from the fact that we will never know them directly. As the great Aldo Leopold wrote, “There will always be pigeons in books and in museums, but these are effigies and images, dead to all hardships and to all delights . . . They live forever by not living at all.”

From my perspective, whether people living today can transform their concern for “book-pigeons” into effective action on behalf of the plants and animals remaining to us is the most important question we face.