The ingredients were there to survive, but to thrive?

Flamingos are a social species that love each other’s company, and No. 492 went off on its own. When a flamingo at the zoo needs medical attention, the keepers will isolate three or four together so the injured bird is more comfortable than it would be alone, Mr. Newland said. Even seeing its own reflection in a mirror can calm a flamingo down.

But great fortune was ahead for No. 492. Soon after it arrived in Texas, it found an unlikely companion: a Caribbean flamingo that, Mr. Newland speculates, may have been blown into the Gulf during a tropical storm. They were seen together as early as 2006 and as recently as 2013.

“Even though they’re two different species, they are enough alike that they would have been more than happy to see each other,” he said. “They’re two lonely birds in kind of a foreign habitat. They’re not supposed to be there, so they have stayed together because there’s a bond.”

Though they’re often referred to as mates, no one knows the sex of either bird. And Mr. Newland said the fact that they’re roughly the same height suggests they’re likely to be the same sex.

Whether they’re best friends or mates, they weren’t together when Mr. Shepard spotted No. 492 in May. It raised the question: Could the Caribbean flamingo have died? Is No. 492 alone again?

Maybe, but Ms. Arengo said there were other explanations. They could have naturally gone their separate ways — a breakup similar to the one with No. 347. Or the other flamingo could have been nearby but out of sight, set to reunite with No. 492 later.

“It’s possible they’re separated and will show up back together again,” she said.

Either way, Mr. Newland said No. 492 could live another 10 to 20 years. Predators include foxes and bobcats, but since flamingos pose little threat to humans and are not considered game birds, No. 492 likely doesn’t have to worry about hunters. Mr. Newland estimated No. 492’s age to be 20, and flamingos in the wild can live into their 40s.