ST. LOUIS — VIEWED from a Cessna 172 high above the Mississippi River, the American bald eagle's rebound from near-extinction shows up with dramatic flair.
On a recent three-hour flight from St. Louis to Quincy, Ill., the World Bird Sanctuary counted 630 eagles soaring above the river's patchy ice, diving for fish, and landing gracefully in tree branches high above the water.
Missouri now has the second-highest population of wintering eagles among the lower 48 states, behind Washington. Alaska, of course, has the most overall.
Last year, the Show Me State hosted more than 2,400 wintering bald eagles. This contrasts with the late 1970s, when only 500 or 600 birds came to the state, according to Jim Wilson, an ornithologist with the Missouri Department of Conservation.
Credit for the national bird's comeback goes to the federal Endangered Species Act of 1973. Since then, the majestic birds have gone forth and multiplied under federal protection. In 1994, their status shifted from ''endangered'' to ''threatened.'' With population increases have come growing crowds of bird-watchers to wintering grounds that stretch from Oregon to Kentucky.
Meanwhile, some environmentalists say the Endangered Species Act itself is threatened. The Republican Congress is considering a plan to break up the federal act and hand its responsibilities out to individual states.
A coalition of environmental groups criticizes the plan as dangerous. If the bald eagle had only been protected in some states, they say, it might not have steered clear of extinction.
The renaissance of the species actually dates back to 1972, when the pesticide DDT was banned. When eagles and other birds ate fish contaminated with DDT, they laid thin, fragile eggs that often broke before hatching. Despite on-going hazards such as loss of habitat and shootings, the eagle population began to increase immediately after the DDT ban.
The eagles that spend winters in Missouri migrate south from their breeding grounds in Canada, northern Wisconsin, Michigan, and Minnesota. The cold weather and frozen rivers drive the birds south in search of fish, their main food source.
The wintering bald eagles have taken over some of the abandoned riverfront land evacuated after the region's devastating flood of 1993. The birds also congregate near the locks and dams along the lower Mississippi River, where they find fish in the constantly churning water.
During the winter, the World Bird Sanctuary conducts regular eagle-counting flights along the river. ''It's much more accurate to count the birds from the air,'' says Jeffrey Meshach, the sanctuary's chief eagle counter. The sky view allows for counting birds perched on islands, sitting on ice floes, or otherwise out of view.
The process of counting eagles from the air is similar to playing the search-and-find game ''Where's Waldo'' at arm's length for three hours; it takes concentration. But the view of a flying eagle - with a wingspan reaching eight feet across and white head and tail feathers gleaming in the sun - makes it all worthwhile.
These days the eagle counters have little time to revel in the beauty of the birds they see, however. They're too busy counting. The eagle population's increase in eastern Missouri and southern Illinois has been dramatic.
''When we first started the eagle census here, if we saw 100 birds that was a great day,'' says Walter Crawford, director of the sanctuary. ''Last year, we had one day where we saw 1,200.''
Despite the progress, Mr. Crawford says, ''we don't want people to be lulled into a false sense of security.'' Humans are now the biggest threat to bald eagles, he says. His group is currently treating three eagles for gunshot wounds.
Other threats to the species include habitat destruction and contaminated agricultural runoff. ''Even though the population is coming back in tremendous numbers,'' Crawford warns, ''these factors are putting enormous pressure on the species.''