After just three years as a conservation area, BLM wildlife biologist David Krueper found that counts of song sparrows, summer tanagers and warblers had increased by up to 6,000 percent. The prestigious Cooper Ornithological Society published Krueper's research, the first in the country to chart recovery of birds along a cattle-free stream. It has the nation's highest mammalian diversity. The river graced Life magazine's list of America's Last Great Places. It has become an economic asset, attracting tens of thousands of birdwatchers a year and lots of good publicity.
Today there is even talk of reintroducing beaver to the desert river.
But the San Pedro flies warning flags. Two summers ago, Arizona State University ecologists found that the northern and southern ends of the conservation area showed dehydration. Among the missing were cattail and bulrush and marsh grasses that had sprouted elsewhere along the river after cows were removed. Baby cottonwoods and willows weren't growing in stretches where the water table had dropped as little as three feet or so beneath the river. In the desert, even established cottonwood trees and cattail marshes don't have much safety margin.