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#07-222 August 13, 2007

Hammock islands offer important habitat for birds

Previously unsuspected numbers of birds have been discovered breeding on the state’s hammock islands. A recently completed survey of these islands has revealed a high ecological significance for these often-small uplands, particularly as important habitats for many species of birds, including a coastal favorite, the painted bunting.

The survey, led by S.C. Department of Natural Resources biologist, Billy McCord, was initiated in 2003 with funding support from S.C. Department of Health and Environmental Control’s Office of CoastalPainted Bunting Resource Management. Continued funding was provided by the State Wildlife Grants program, enabling McCord to survey additional hammock islands. McCord, along with survey volunteers and other partners, examined 130 hammock islands located along the coast from Huntington Beach south to Spring Island. The islands, classified by their occurrence between barrier islands and the mainland, are surrounded by wetlands or tidally influenced water, and are typically less than 1,000 acres in size. About 3,500 hammock islands occur along the South Carolina coast, ranging in size from 0.1 acres to 1000 acres. The diversity in flora and fauna that they offer serves as an attractive habitat for a variety of coastal birds that come to these isolated islands for resting, nesting, roosting and foraging.

According to McCord, "Through the extensive survey, we found these habitats to be much more biologically diverse than what we originally thought before this undertaking."

Scientists have recorded more than 530 species of plants, 224 vertebrate species, 90 invertebrates (limited primarily to butterflies and dragonflies) and notably, 161 species of birds.  Of those birds observed, 59 of the species were found to be using the hammock islands as breeding grounds. The methodology for this survey consisted of visiting as many islands as was practical on multiple occasions to make observations at different times throughout the year. McCord described the survey technique as a type of "foraging," allowing scientists to take a largely qualitative approach to inventorying a broad diversity of plants and animals that thrive on the hammock islands. Many volunteers participated in surveys, but the most consistent participation was provided by employees of U.S. Fish and Wildlife Service (Charleston office), Kiawah Island Community Association, and Spring Island Trust.

Hammocks provide a high diversity of habitats and plant communities including isolated wetlands, forests, shrub thickets and grasslands.  Unique and rare plant communities were found in association with Native American shell deposits. McCord said, "Since many bird species are habitat specialists, bird species diversity in any area is likely correlated with habitat diversity." McCord’s observations show that Eastern Painted Bunting favors the mixed habitat types associated with hammocks, and they were found to frequently use the areas as both migratory resting stops and breeding grounds. The Eastern Painted Bunting is among South Carolina’s list of highest priority species in need of conservation, as well as being on the Partners in Flight watch list for priority protection. Painted buntings are one of the most colorful and sought after birds by birdwatchers in South Carolina. McCord observed painted buntings on 22 of the 25 hammock islands that were surveyed during the bunting’s breeding season in 2004, revealing that these birds are able to find desirable breeding habitat on most hammock islands of two acres or larger.

In addition to painted bunting observations, McCord noted that 10 species of wading birds use hammocks, including nesting observations for Great Blue Heron, Great Egret, Snowy Egret, Black-crowned Night-heron, Yellow-crowned Night-heron and Green Heron. Hammocks are used for resting, especially during high tides, serve as roosting sites, provide desirable nesting areas, and adjacent tidal wetlands and enclosed isolated wetlands offer many food resources. The federally endangered Wood Stork has also been shown to extensively use isolated hammock islands as resting and roosting sites. "Resting of many species of wading birds," according to McCord, "was observed to be more prevalent on isolated hammocks in the Charleston area than on hammocks further south in the protected ACE Basin (Ashepoo, Combahee and Edisto Basin), which provides evidence that habitat loss and disturbance can influence the extent to which these species use the hammock islands."

Nearctic-Neotropical migratory land birds breed primarily in North America north of Mexico and winter primarily from Mexico into more tropical areas of the Caribbean and Central and South America.  The Nearctic-Neotropical group includes many species that breed and are resident in South Carolina during spring and summer, including Eastern Painted Bunting, Indigo Bunting, Summer Tanager, Orchard Oriole, Yellow-throated Warbler and Prairie Warbler. Other members of this migratory bird group breed north or west of coastal South Carolina, some primarily in mountainous areas, and only occur along the state’s coast as transients during fall and spring migration. Nearctic-Neotropical birds migrate primarily at night and are highly dependent upon forested coastal uplands for rest, shelter and refueling during daylight. Again, the high diversity of plant communities and habitats on hammock islands provide invaluable shelter and food resources, including abundant insects, fruits and seeds, for a high diversity of migratory birds. McCord recorded 59 species of transient birds using the hammock islands during migration, including additional highest conservation priority species for the state such as Prairie Warbler and Wood Thrush.

Birds of prey, marsh birds, shorebirds and resident, non-migratory land birds also inhabit coastal hammock islands. Birds of prey, including Bald Eagle, Great Horned Owl and Osprey were found nesting on the hammock islands. Twenty-six of the 144 Bald Eagle nesting territories in South Carolina’s coastal area are on hammock islands. Common resident land birds most often encountered, according to McCord, included the Northern Cardinal, Red-bellied Woodpecker, Carolina Chickadee, Downy Woodpecker and Carolina Wren.

As development continues to alter the traditional habitat along the marshlands, many bird species have likely sought isolated habitat on these hammocks.  The survey observations show that these sensitive and ecologically important areas are favorable habitats for a diverse range of fauna.

Distribution of Hammock Islands in SC by Coastal County:

Horry  23
Georgetown 130
Berkeley 86
Dorchester 26
Charleston 1321
Colleton 278
Beaufort 1418
Jasper 187
Total 3469

 

 

 

 

 

Species of birds identified as rare or at-risk in SC that were observed during the survey:

Land birds 21
Water birds 3
Marsh birds 2
Wading birds 10
Shorebirds 7

DNR protects and manages South Carolina’s natural resources by making wise and balanced decisions for the benefit of the state’s natural resources and its people.


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