Fort Myers, Florida (News-Press) -- Wood stork news in South Florida is good, but it could have been better.
For the first time since 2009, the endangered birds nested Corkscrew Swamp Sanctuary, historically the largest wood stork breeding colony in North America: Storks built 200 successful nests and fledged 300 chicks; in the Everglades, wood storks built about 1,400 nests.
"Nesting occurred early, and the vast majority of the chicks left the nest with several weeks between fledging and the start of rainy season," sanctuary director Jason Lauritsen said. "So they stand a good chance of making to adult breeding age. That's the goal. You can count nests and fledglings, but if they don't make it to be breeders, it doesn't matter."
Nesting success for wood storks depends on a rainfall formula:
• Step 1: Heavy rains in the summer fill wetlands in and around Corkscrew, so fish, crawfish and other good wood stork food breed in high numbers.
• Step 2: The area gets little rain in the fall and winter, so the wetlands "dry down," and the stork food becomes highly concentrated in small, shallow pools. That makes prey easy to catch, so adult storks can get plenty to feed themselves and their chicks.
But sometimes the formula breaks down:
If not enough rain falls in the summer, prey items are scarce, so the storks won't nest.
If too much rain falls in the dry season, the wetlands don't dry down to concentrate prey, so the storks won't nest.
If the wetlands dry down late, storks might nest late, and chicks will be in the nest when summer rains fall (nesting season is five months long). In that case, wetlands fill with water, and prey disperse and become difficult to catch. Adult wood storks can't get enough food to feed themselves and their chicks, so they abandon the nests.
If the area gets heavy rain during the dry season, wetlands fill up, and storks abandon nests. When rains fill the wetlands while birds are still nesting, it's called a reversal.
Weather cooperated at the beginning of this nesting season.
"We had a little over 55 inches of rain at Corkscrew from June through Oct. 1; that's almost a year's worth of rain," Lauritsen said. "The water came up quick and pushed into places it usually doesn't, so fish and crayfish pushed into places they usually don't go. That's a recipe for early nesting."
Right on schedule, the wetlands started drying down; storks started nesting in mid-December, and by late January, 270 nests were in sanctuary trees.
But heavy rains at the end of January raised water levels in the wetlands, and some storks abandoned their nests; the conditions might have discouraged other storks from building nests, Lauritsen said.
"The only thing that didn't work out was that one big weather system," he said. "If not for that late January rain, I imagine the colony would have continued to grow."
Although Corkscrew's wood stork nesting season was a success, the numbers were comparatively low.
In 2009, the last time wood storks nested in Corkscrew, 1,120 nests produced 2,570 fledglings.
Even that number is small compared to the wood stork nests of more than 30 years ago.
Since 1958, the first year Corkscrew wood stork nesting data were recorded, the Top 5 nesting years were all before 1980: 1961 (6,000 nests, 17,000 fledglings), 1960 (4,760 nests, 13,724 fledglings), 1959 and 1979 (4,505 nests, 8,910 fledglings) and 1967 (3,680 nests, 7,350 fledglings).
The reason for greater nesting success in the past is better habitat.
"Even when we get the right conditions, we still don't grow as many wood storks," Lauritsen said. "When we started draining the landscape, we lost the carrying capacity, or a region's ability to support a species, in this case, wood storks. We've just lost too many shallow wetlands, so South Florida can't grow the number of wood storks it used to."
Like Corkscrew, those areas had a reversal in January, and then they had a second reversal in February, so some wood storks abandoned nests, said Mark Cook, a water district environmental scientist.
"The birds held out quite a while, a good few weeks," Cook said. "Then we saw nests dying, with dead chicks. In one colony, the nests dropped from 350 to 100.
Because the water was too high for easy wood stork foraging, the water district lowered water levels in some areas.
"To some extend, that worked," Cook said. "What surprised us is that it worked so well, and many birds started nesting again in February and March. Within the last month, we saw nests with eggs and very young chicks."
If South Florida gets normal summer rains, many of the chicks from those nests won't survive.
"The sad part here is we were expecting a very good year for wood storks," Cook said. "We had thousands of birds in the system. The wood storks were foraging well, but then the reversals came. This could have been a good year, if it hadn't been messed up right in the middle."