Two young whooping crane couples laid eggs this year, bringing hope and disappointment to biologists trying to establish a flock of the elegant endangered birds in southwest Louisiana.

At least one egg was fertile. However, heavy rains flooded the nest, so it never hatched, said biologist Sara Zimorski of Louisiana’s Department of Wildlife and Fisheries.

Whooping cranes are among the world’s most endangered birds. About 600 graceful, 5-foot-tall cranes all are descendants of a flock that migrates between Texas and Canada. That flock now numbers 310; another 95 are in a flock that ultralight pilots taught to migrate between Wisconsin and Florida. Louisiana has 40. Most of the 160 captive whoopers are in Laurel, Maryland.

Louisiana’s known fertile pair — named with scientific but unromantic precision, L1-11 and L6-11 — were one of two pairs spotted copulating this year at White Lake Wildlife Conservation Area, where they were released in 2011.

“I was starting to feel a little frustrated — ‘Why don’t you guys nest?’ Then they did,” Zimorski said Tuesday.

Less than a week later came an April deluge.

“Cranes will try and build up their nest in response to rising water. But there’s nothing they could do to keep up with 10 inches of rain in four days,” Zimorski said.

Biologists recovered one egg and a fragment of another from the abandoned nest.

An incubator couldn’t save the embryo.

Whooping cranes mate for life and take turns sitting on their eggs. L6-11 hasn’t had any more eggs, but there’s time, Zimorski said.

The other eggs, laid by female L7-11, were infertile, like two pairs she and L8-11 incubated last year. Those birds, now 4 years old, were the first in 75 years to lay eggs in the wild in Louisiana.

Their big nest mounds have been built in crawfish ponds owned by a farmer who told biologists when the eggs were laid in late February and early March.

Whooping crane eggs usually take about 30 days to hatch. Just to be sure, biologists waited 40 days before collecting them.

Zimorski said cranes will move away from a nest to draw predators away from the eggs. “Once they actually realize we’re coming close to the nest, they high-tail it back to defend it,” she said.

They didn’t attack, she said.

About 2½ weeks later, they built a new nest and laid two eggs.

If these prove infertile, the birds may just be too young, Zimorski said.

A pair released in Wisconsin hatched a chick their fourth nesting year, after four years of infertile eggs, she said.

Two other mated pairs have formed in Louisiana. A few other pairs may be in the works, Zimorski said, but those birds, 2 and 3 years old, could be considered still dating.