Grad student assesses wading bird use of salt marshesWhen Rhode Island’s first nesting egrets set up housekeeping on Little Gould Island in Narragansett Bay in 1964, it was part of the range expansion of six species of long-legged wading birds that have since colonized four other islands in the Bay. While the nesting islands — including Hope, Dyer, Rose, and Big Gould — were subsequently protected by the state and local environmental groups, little was known about the habitat these birds use for feeding.
Until now.
URI graduate student Carol Trocki is beginning the second year of her research to determine exactly where the birds go to find food and what kind of habitat they prefer.
“I want to determine the characteristics of the places they prefer to feed at,” said the 24-year-old environmental scientist. “This will help to guide wetlands restoration plans and help to prioritize those salt marshes that should be protected.”
From May to September last year, Trocki monitored 15 salt marshes along the Rhode Island coast from Little Compton to South Kingstown. On each visit, she identified all of the wading birds present - great egret, snowy egret, cattle egret, little blue heron, glossy ibis, and black-crowned night heron — and established where in the marsh they were located, what habitat they were using, and what they were doing (feeding, preening, loafing, or flying).
All the birds feed on small fish and invertebrates found in salt marshes. They also feed along the shore, in freshwater marshes, and, in some cases, in active farmlands. Because the nesting islands are small and rocky, it’s important that feeding habitat exist close by.
After the first year of study, Trocki found that the most important factor affecting the birds’ choice of which salt marsh to use was the amount of appropriate foraging habitat available. “The birds especially like the shallow, open water at the edge of the marsh where it’s the right depth for feeding,” she said. “During the breeding season I found a significant relationship between how much open water edge habitat there was and how many birds we found there.”
According to Trocki, who also works at URI as coordinator of the Coastal Fellows Program, during the breeding season the adult birds are under great pressure to find food for their fast-growing young. Eighty-three percent of the birds observed using the marshes during the breeding season were foraging. But after the breeding season ended in July, just 57 percent of the birds observed were looking for food. During this post-breeding season, the number of birds using the marshes increased significantly, due in part to the dispersal of juvenile birds from their nesting islands to the marshes and due also to the movement of other birds into the area. By the end of September, most of the birds have migrated south for the winter.
Trocki said that the results of her research will be useful to agencies or organizations that are interested in creating or restoring salt marsh habitat. “With my data they can answer the question, ‘what should I make my salt marsh like if I want wading birds there?’” she said.
By Todd McLeish
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