South Florida, including Everglades National Park, has seen a precipitous decline in nesting success among wading birds, according to a report by the South Florida Water Management District.

The region is one of the country's largest and most-important wading bird nesting areas, according to the American Bird Conservancy. However, the latest nesting survey shows a decline of 39 percent below ten-year averages, the group says.

"This weather-induced decline bucks a trend dating to 1985 of growing bird populations in South Florida as a result of restoration of water flows in the Everglades, and reaffirms the need for speeding completion of the project," the Conservancy said.

The report says that an estimated 26,395 wading bird nests were initiated throughout south Florida during the 2012 nesting season. Not only is that a 39 percent decline relative to the decadal average, but a 66 percent decline relative to the 77,505 nests for 2009, which was the best nesting year on record in south Florida since the 1940s, the ABC said.

While the 2012 number is comparable to that of 2011 (26,452) and 2010 (21,885), it is the third consecutive year of relatively poor nesting effort in south Florida, the group added.

"These numbers are alarming because we are talking about extremely important bird breeding grounds on a national level and we’re looking at three years of poor breeding success,” said Kacy Ray, Beach Nesting Bird Conservation Officer for American Bird Conservancy, one of the nation’s leading bird conservation organizations. “Restoring water flows in the Everglades will re-establish prey production and availability across the landscape that, in turn, will support the return of large successful wading bird colonies to the traditional rookeries downstream.”

All species of wading birds suffered reduced nest numbers relative to the past ten years, but the extent of the decrease varied among species. Of particular concern are nesting failures of the endangered Wood Stork, which declined 44 percent; White Ibises (39 percent) and Snowy Egrets (56 percent) also suffered significant declines. There was also limited nesting by Little Blue Herons and Tricolored Herons (only 89 and 412 nests, respectively), which continues a steep and steady decline in nesting activity for these two species during the past eight years.

The federally Endangered Wood Stork fared particularly poorly and it is thought that all 820 nests failed or were abandoned. By contrast, anecdotal observations suggested that Great Egrets, Snowy Egrets and White Ibises in Everglades National Park were relatively successful. Another region that experienced poor nesting success was Lake Okeechobee, where most colonies experienced complete or extensive nest failure.

This contrasts with long-term trends showing population increases for Wood Storks, Snowy Egrets, Great Egrets, White Ibis, Small White Heron, Great Blue Heron, and Roseate Spoonbill, the ABC said.

Wading bird breeding patterns in south Florida are driven largely by hydrology through its influence on the production of prey and their vulnerability to predation. The 2012 breeding season was preceded by several drought years followed by a relatively wet season. Such conditions generally limit the production of small fishes that the birds feed upon.

“To restore and manage for wading bird populations in the Everglades, the right amount of water at the right time and the right place is needed to optimize the availability of aquatic prey species (small fishes and crayfish). The long-term monitoring programs in this report (both avian and prey related) are critical to this end,” said Mark Cook of the South Florida Water Management District. “We need to know what’s happening, why it’s happening and what’s working if restoration efforts are to be targeted effectively. These programs have made considerable advancements in our knowledge of wading bird ecology in recent years, although much still remains to be learned about getting the water right for the birds.”