A decline in small herons and egrets that nest and forage among the Everglades wetlands and tree islands could mean work to restore the troubled ecosystem is not moving fast enough.
An annual survey by the South Florida Water Management District released Thursday found that in 2014, five years after a record rebound, the overall number of nests in and around refuges, wildlife sanctuaries and water conservation areas was down by 60 percent — 28 percent lower than in 2013. The drop in Everglades nests for little blue herons, tricolored herons and snowy egrets was particularly troubling: nests that numbered over 1,000 a decade ago were down to about 130 last year.
Biologists monitor the birds because their health is so closely tied to Everglades hydrology. When the birds do well, the ecosystem is in good shape.
“These birds tell the story of how we’re doing with restoration,” said Tabitha Cale of Audubon Florida.
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Biologists believe rain played a key factor in the decline. Heavy rain in 2013 probably produced more fish that compete with wading birds for smaller prey like crayfish. More rain between February and April also spread prey normally concentrated in small pockets of water.
While the numbers were down overall, the woodstork, protected as a threatened species, made a surprise comeback, returning to the Corkscrew Swamp east of Naples for the first time in seven years, Cale said. Ibises, storks and great egrets have also increased over the last 15 years.
Why the bird populations rise and fall remains a bit of mystery, tied to water level, rain and food supplies. Scientists were glad to see birds nesting more consistently along the coast, but say numbers need to increase.
Rising sea levels could also be playing a part. Audubon scientists say roseate spoonbills appear to have fled coastal rookeries in Florida Bay in search of higher ground. Only 126 spoonbill nests were counted in the bay, down from 367. In the central Everglades, the number fell from more than 200 to 50, the report said.
“If anything, this decline in wading birds shows we need to step up the pace [of restoration work] to make sure we don’t lose everything magical about this ecosystem,” Cale said.