Take a walk in a Tokyo garden -- particularly an undisturbed, crow-haunted one such as the Institute for Nature Study's park in Meguro -- and you might find this hard to believe, but the world's bird population is shrinking. According to a report released to coincide with BirdLife International's quadrennial world conference in South Africa last week, one in eight of the world's bird species are threatened with extinction.

That is over 1,200 species. And the rate of extinction is accelerating. In the last 500 years, 129 species were declared extinct; today, 179 species are critically endangered and another 344 are at "very high risk" of extinction, the report says. Some pockets of the planet are so inhospitable they actually face a future in which, in the poet John Keats' phrase for a fatally stricken landscape, "no birds sing."

Anyone who saw last year's documentary "Winged Migration" will have an inkling of what such a loss would represent. For three years, the filmmakers tracked the migratory paths of birds, from pole to pole and numerous destinations in between, accompanying the flocks in gliders, balloons and ultralight, motorized aircraft. The result was a bird's-eye-view of Earth as a place alive with flying, soaring, hopping, darting creatures, extraordinarily various and beautiful. Crisscrossing and encircling the planet, birds weave what the film portrayed as a mysterious, protective web of life around and above us. As long as birds are safe, the movie implied, all the diverse forms of life below are somehow safe as well.