In our modern world we are accustomed to seeing large-bodied species in decline. Elephants, rhinos, tigers, whales, sharks, big trees -- the list goes on and on.
But there's another large biological phenomenon that is at least as vulnerable -- the great animal migrations.
Seasonal movements are crucial to the survival of most migratory animals. And nearly everywhere one looks, migrations are collapsing.
In the plains of the American Midwest, the once-thunderous migrations of Bison and other large wildlife have virtually disappeared.
In northern Cambodia, the great migration of Asian Elephants, Gaur, and other large mammals -- known as the "Serengeti of Indochina" -- have vanished.
On the island of Borneo, large-scale movements of Bearded Pigs and Sun Bears -- in response to pulses of fruit availability -- are collapsing and causing massive animal die-offs, as poignantly illustrated by this video of a starving Sun Bear.
In the western Pacific, stunning annual migrations of shorebirds -- with some species traversing from Alaska to Australia and back each year -- are being rapidly eroded by runaway development of coastal shorebird-foraging sites, most dramatically in China and the Koreas.
In the Mojave Desert, a proposed solar-energy project would imperil the seasonal migration of Bighorn Sheep -- as highlighted recently by ALERT member Thomas Lovejoy and Harvard biologist Edward Wilson.
And in the iconic Serergeti Plain of Africa, a proposed highway would slice directly across the route of migrating wildebeest and scores of other wildlife species, potentially imperiling the greatest surviving migration on Earth.
David Wilcove at Princeton University has long studied animal migrations and their demise. He makes a key observation: nobody has ever set out to destroy a great migration.
Instead, migrating animals are being forced to endure an ever-growing array of human pressures -- new roads, dams, farms, cities, overhunting, persecution, and myriad other threats.
And then, one day -- seemingly without warning -- the migration just stops. The salmon runs collapse. The last surviving Passenger Pigeon disappears.
As humans gobble up ever more of the planet, saving the Earth's last great migrations is going to be one of the greatest of all challenges facing conservationists.
That it is an enormous challenge makes it not one bit less important.