Collapse and Distillation
Things fall apart–but why? And how? Perhaps it is mere
anarchy loosed on the world, but Charlie Hadlock has other ideas. In Six Sources of Collapse, published last
year by MAA, Hadlock describes a half-dozen mechanisms that lead to collapses
that seem abrupt.
He begins with the humble passenger pigeon. Two centuries
ago North America was, literally, aswarm with passenger pigeons. In 1813
Aubudon observed a flock that obscured the midday sun and took three days to
pass. Alexander Wilson once observed a flock that he estimated contained more
than 2 billion individual birds; that is eight times the current estimate for
the world’s total rock pigeon population. A single nesting ground near Sparta,
Wisconsin, covered 850 square miles and housed an estimated hundred million
birds. Flocks were so thick that folks hunted by swinging a stick in the air
and picking up what came down.
It seems hard to credit that we hunted such abundance to
complete extinction. (The last known passenger pigeon, Martha, died at the
Cincinnati Zoo in 1914.) Hadlock explains the mechanism as the blank and
pitiless result of evolution–the birds had evolved to live in enormous flocks.
Their reproductive success depended on that, and these gigantic flocks were
well adapted to a completely forested eastern United States. A flock of half a
billion birds could denude and befoul a patch of forest in a few days, then
move on to the next patch. Human settlement and forest clearing limited the
available resources for this behavior. The combined effect of thinned forest
and thinned flock (from a tide of hunting) led to dramatic population collapse.
