MIAMI (AP) – The Everglades’ graceful wading birds such as the white ibis and snowy egret are breeding at a rate unmatched since 1940, a survey found.

But scientists cautioned that this year’s increase in nests is probably caused more by favourable weather than by conservation efforts. And more breeding has not yet translated into more birds.

Still, the scientists who produced the annual South Florida Wading Bird Report see the increase as a sign that the Everglades’ fauna can recover from decades of development that has disturbed the natural flow of water.

Wading birds are excellent indicators of the Everglades’ overall health because they travel over the southeastern United States before deciding where to breed, said John Ogden, the South Florida Water Management District’s chief representative for Everglades restoration.

“It’s a good sign that the Everglades is their first choice,” Ogden said.

The report released Thursday found 68,750 wading bird nests this year in the Everglades and surrounding areas, about twice the average recorded over the past decade. Included in the figures for the January-to-May breeding season are nests of white ibises, snowy egrets, herons, wood storks and roseate spoonbills.

“Even with the ideal conditions we’ve had, we wouldn’t have expected this many birds,” said Dale Gawlik, the report’s editor and an environmental scientist with the water management district.

Gawlik and Ogden attributed the increase to dry weather. Unseasonably rainy weather raises water levels, causing birds to abandon some nests and making the fish they feed on harder to reach.

“The huge question right now: Is this just some kind of spike because of special conditions that we can’t sustain?” Ogden said.

The increase in nesting is also a result of better water management by the district, said Stuart Pimm, an Everglades researcher and ecology professor at Columbia University. He said district officials learned from their mistakes in 1993 and 1995, when they released large amounts of water into the Everglades during the dry seasons.

A 30-year, US$8-billion project to restore the Everglades is just now getting under way. The joint federal-state plan, approved in 2000, includes more than 60 public works projects to restore a more natural flow of water through the Everglades.

Wading birds nearly went extinct in the early 1900s because of plume hunters. By the 1930s and ’40s, after a public outcry brought a crackdown on hunting, breeding rebounded, and the number of nests ranged from 35,000 to more than 200,000 each year.

But after the 1940s, drainage canals, flood-control levees and rampant development reduced the Everglades by half, sending wading-bird populations plummeting.