AUSTWELL, Texas — One of the most beloved groups of winter Texans is back, in the largest number in a century and with a record 45 youngsters in tow, including an even rarer seven pairs of twins.

They flew 2,400 miles from Canada’s Northwest Territories and can be seen munching on blue crabs and bright red-orange wolfberries among the marshes of the Aransas National Wildlife Refuge.

The whooping crane, the tallest bird in North America, whose numbers dwindled to fewer than 20 in 1941, is not only back from the brink of extinction but also thriving — a comeback story, federal wildlife officials say, that illustrates how a coordinated conservation effort can save a species.

“The whooping crane continues to mirror the success of endangered species recovery when man sets his mind to it,” the national whooping crane coordinator for the U.S. Fish and Wildlife Service, Tom Stehn, said. “We have come a long way, but we do have a long, long way to go.”

This year, the nation’s only natural wild population of whooping cranes reached a milestone. Mr. Stehn’s mid-December census of the migratory crane flock at the wildlife refuge, where he is based, numbered 237. Combined with the number of birds in captivity in three special flocks raised for reintroduction to the wild and those in zoos, the crane population now numbers 518. This is the first time in more than a century that whooping cranes have numbered more than 500.

Deboarding from the tour boat Skimmer at Aransas one sunny morning a few days before Christmas, Mike Dixon explained why he and his family drove in from West Texas just to see the huge white birds and their rusty brown chicks.

“Those birds out there are the result of a whole lot of effort, money, and concern to save a species, and that’s exciting,” he said.

Recovery efforts date to 1938, a year after the federal government established the Aransas Wildlife Refuge along the south Texas Gulf Coast. The salt marsh was known to be the winter home of several species of migratory birds, including the majestic whooping crane, with its long sinuous neck, height of 5 feet, and wingspan of 7 feet.

The cranes numbered just over 20 in the first census, in 1938. By 1941, the migratory flock was down to 15, largely because of shooting, the conversion of grasslands to agriculture, and the draining of wetlands.

“This species was virtually four nesting females away from extinction, and that’s why this is so significant,” Mr. Stehn said. “It was just such a close call, such an incredibly close call.”

The crane’s breeding grounds were unknown until 1954, when a fire crew flying over Wood Buffalo National Park in Canada’s Northwest Territories accidentally discovered the migratory flock. In America, the whooping crane was listed as a threatened species in 1968 and moved to the endangered list two years later, prompting a series of efforts to increase the flock’s size.

In 2001, the Whooping Crane Eastern Partnership, an American-Canadian partnership of governments, nonprofit organizations, citizens, and corporations, developed a method to teach captive-raised whoopers how to migrate so they could be introduced to the wild. Since then, young cranes have been led in migration every fall by gliders flying from the Necedah National Wildlife Refuge in Wisconsin to the Chassahowitzka National Wildlife Refuge in Florida, 1,200 miles away. The cranes return on their own in the spring.