The Natural Georgia Series: Barrier Island
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The Natural Georgia Series: Barrier Island |
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In the 1800s in the southeastern part of the United States there were passenger pigeons and Carolina parakeets, but now the birds are extinct. In 1810 an early American naturalist, Alexander Wilson, recorded 2 billion passenger pigeons migrating south for the winter. The birds were so plentiful that when they flew overhead in flocks, it would take an hour for them to pass. The birds were hunted and as their numbers dropped drastically, they were placed in zoos to try to reestablish the flock. But by 1914 the last known passenger pigeon died at the Cincinnati Zoological Garden. The last Carolina parakeet died the same year. North America's only known parrot was hunted for its bright plumage of yellow, green, and orange and sold to milliners. Hunting, habitat destruction, and behavior patterns that limited its dispersal in times of danger led to the Carolina parakeet's extinction. Based on the stories of these birds and others, biologists now believe that once a bird species' population drops below a certain threshold, nothing can be done to save it.
The Atlantic least tern, the smallest of the terns, has faced many of the same threats that led to the extinction of the Carolina parakeet and passenger pigeon. Least terns also have been hunted and sold to milliners. Their white plumage, forked tail, and petite size made the birds popular. They were shot, stuffed, and used as decorations for hats from the 1870s to the early 1900s. The birds were easy to shoot since they hover protectively above their nests. Today, on the Georgia barrier islands and in other southeastern areas where they reside, least terns are protected from hunting. But least terns' habitat is threatened, and their numbers are declining. Keeping the birds from becoming extinct will require finding ways humans and least terns can live in harmony.
Least terns nest on beaches and dunes, but as their habitat diminished, they have moved to dredge sites and now to rooftops of large buildings to nest. This change in nesting sites has been attributed to an increase in human population in beach areas, to hurricane flooding, and to predators.
This change in nesting sites could be the stage before extinction if history is any clue. No one knows for sure. Studies were not performed on the passenger pigeon and the Carolina parakeet to know if changes in habitat and nesting sites and overhunting were the only reasons for extinction. That is why recent studies being made on birds, their nesting sites, their migratory patterns, and their life cycles are important. Information gathered may answer more than just questions about the life cycles of birds on earth. The information may provide clues as to how humans must adapt to a changing environment.
What we do know is that where the birds stop in their migration patterns is important to their survival. We know that at certain numbers, birds stop breeding and die out. We know that we cannot risk interrupting life cycles because we cannot predict the consequences.
Least terns are listed as rare along the Georgia coast. The most extreme listing would be endangered, then threatened, then rare. Rare means the birds should be protected because of their scarcity. The Georgia Board of Natural Resources determines that a species is rare based on declining populations, trends, and habitat threats.
There are several colonies of 300 pairs of least terns, but more colonies are smaller with only a few dozen pairs. These birds are like the canaries of the mines, says Royce Hayes, superintendent of the St. Catherines Island Foundation. "What's happening to the birds will happen to us," says Hayes. "Miners would carry canaries down into the shafts, and if the birds couldn't breathe, the men knew they couldn't. Today's 'canaries of the mines' are being studied for the impact the change of the environment may be having on them and ultimately on humans. Birds are sensitive," says Hayes, "if they can't survive the changes in the environment, then how will humans?"
Atlantic least terns (Sterna antillarum) are 8.5 to 9.5 inches in size. They are one species of many terns that are related to the gulls. The Caspian tern is the largest. The Atlantic least terns are the smallest. Unlike other species of terns, the least terns do not mix species or mix colonies. The least tern has a broad white forehead framed by a black crown and black line running from the crown through the eye to the base of the bill. The mantle and the short but strongly forked tail are pearl gray. A long, thin wedge of black up the leading edge of the outer wing is conspicuous in flight. The narrowly black-tipped bill and the feet are yellow. The birds are tenacious and obnoxious and put up a good fight when humans or predators invade their nesting area.
Life cycles of least terns are between 20 to 30 years. Least terns prefer to nest on open mainland or barrier island beaches covered with a coarse substrate of sand, shells, or small stones. Biologists have suggested that terns will readily abandon sites that fail due to habitat loss and human disturbance. The nests are placed where there is little vegetation and where the least tern can see predators. Least terns do not add materials to their nests. The barrier islands are ideal nesting spots because the islands are often exposed to storms and high tides, which limit denser vegetation from becoming established. This lack of vegetation also limits larger predators of least terns, like raccoons and opossums, from becoming established on the islands. Least terns prefer marginal shoreline habitat.
Once the nesting site is established, the female least tern lays one or two jelly-bean-size eggs. Both parents incubate the eggs. Least terns nest from April to the end of July. The birds are visually cued so once the chicks hatch, the parent will take the eggshells and drop them away from the nest. If the eggs are lost, the least terns will re-nest and can re-nest as many as three times in a season. However, as August approaches the birds begin to lose their nesting instinct. Birds that practice late nesting will abandon chicks in the nest in August and migrate to the south, to the West Indies, Central America, and the northern coast of South America.
Least terns do appear to have a ranking within their colony. The older, more experienced birds will nest in the middle of the colony. These birds seem to be able to detect slightly elevated land that will protect their nests against high tides, and they will locate their nests near driftwood to provide shade in the hot summer. These rankings have been observed by Sara Schweitzer, a wildlife ecologist with the University of Georgia. When predators visit, the birds will mob-swoop down and around the visitors trying to scare them off. Larger tern species can hurt a human through mobbing, but least terns are so small they will come near the human but not make contact. Known predators include crows, dogs, raccoons, cats, feral cats, coyotes, and owls. Owls prey on the least terns at night when the birds will not mob.
Least terns do not nest the first year. They stay in the winter migratory area until the second season. There is a spectacular in-flight courtship. Most often viewed, though, are the beach dances. "They do their little dance on the beach with wings up, wings down, shuffle in the sand for a step or two and then voice a harsh 'kip, kip, kip' sound," says Royce Hayes. The birds have certain sounds to which they respond. Least terns can identify each other through sound. Schweitzer has observed a least tern flying into a large colony with a fish, calling out with a shrill "zreeep," and having only the other parent or chicks of that least tern look up. Male and female least terns look exactly alike.
Least terns fly over shallow water to hunt for minnows or small fish. They fly along the water and hit the water with a belly-buster-type dive. They are not always successful on the first try and may have to try several times to get a fish. They do make a fuss when they bring the fish back to the nest. The bird will bow and posture elegantly when presenting a fish to the mate.
Migration is an important part of some birds' evolutionary life cycle. One species of tern, the arctic tern, will travel the entire length of the globe in one year on its migratory route. "Birds use the entire globe to complete life history, so therefore, conservation is critical to the survival of the species," says Kevin McIntyre, resource manager for Little St. Simons Island.
There are critical stopovers in birds' migrations, says Royce Hayes. "If the birds don't have them, they disappear, they die."
No one knows exactly why some of these migration patterns are important. Studies indicate that the mouth of the Altamaha River is important to the red knots, and St. Catherines Island is important for the wimbrels. Many groups are working to learn more about the migration stopovers of birds. These organizations survey the birds migrating to certain areas, the population trends worldwide, and the timing of the migration. Partners in Flight and West Hemisphere Shorebird Network are two organizations working to help conserve birds that migrate and are declining in number due to loss of habitats. Partners in Flight is an international network of ornithologists, birders, environmental educators, land managers, academic institutions, government agencies, and nongovernmental organizations working together to enhance bird populations. The focus of Partners in Flight began with 255 species of land birds that breed in the United States and Canada and spend the winter south of the United States border. The work of keeping up with the bird populations and the migration stopovers is performed by the Monitoring and Inventory Working Group, one of eight working groups in the Partners in Flight organization. The West Hemisphere Shorebird Network is an international organization based in Massachusetts. Its goal is to identify areas where migratory birds feed and encourage management of the area. For example, the network discovered Reed's beach on the Delaware Bay where red knots feed on horseshoe crabs in the spring and then migrate to Canada.
Ruth Beck, associate professor of biology at William and Mary College in Virginia, has been studying shorebirds for 25 years. She says there is some protection of birds that migrate from the United States through Central America and it is carried out on a country by country basis. There are treaties such as the Migratory Bird Treaty Act, but there are no firm commitments from all countries where shorebirds migrate.
Georgia has the most undeveloped barrier island area in the United States. Other coastal states developed the land extensively. In the United States, 50 percent of the population lives along the coast in an area of land that comprises only 18 percent of the nation's total land area. This is expected to increase 15 percent by the year 2010. The undeveloped area in Georgia provides an opportunity to manage the land to protect wildlife and to offer recreation for humans at the same time. Eight major barrier islands and several smaller barrier islands lie along the Georgia coast. The barrier islands include the following, north to south: Tybee and Little Tybee, Williamson, Petit Chou, Wassaw, Ossabaw, St. Catherines, Blackbeard, Sapelo, Wolf, Little St. Simons Island, Sea Island, St. Simons, Jekyll, Little Cumberland, Cumberland, Cabretta, and Egg.
All of Georgia's approximately 88 miles of ocean beach are located on the seaward side of these islands, and with coastal Georgia's generally mild climate, the barrier islands are highly attractive for recreational and commercial development. The Combined Coastal Management Program and Final Environmental Impact Statement for the State of Georgia, published in 1997, outlines public and private access to the barrier islands. Ten of the islands are in public ownership. With one exception (Jekyll Island), these islands lack causeway access and are designated wildlife management areas, heritage preserves, and undeveloped recreational areas. Tybee Island, Sea Island, St. Simons Island, and Jekyll Island are the only barrier islands directly accessible by automobile and thus the only islands where significant urban development has occurred. Approximately 65 percent of the total upland acreage of the 15 largest barrier islands is in public ownership (36 percent State of Georgia, and 29 percent U.S. Government).
Providing quality management of this barrier island system is significant to the stability of the migratory bird population. Protection in the form of acts includes the Georgia Coastal Management Act, Coastal Marshlands Protection Act, Endangered Wildlife Act, Game and Fish Code, Georgia Heritage Trust Act of 1975 superseded by the Heritage 2000 Program, Georgia Natural Areas Act, and Shore Protection Act.
The Georgia Coastal Management Act enables the Department of Natural Resources to develop and implement plans to manage coastal areas. Tidal wetlands are managed through the Coastal Marshlands Protection Act. Protection of rare, unusual, or other animals in danger of extinction is enforced through the Endangered Wildlife Act. The Georgia Heritage Trust Act of 1975 seeks to preserve certain property in Georgia with unique natural characteristics, special historical value, or particular recreational value. An additional provision is given under the Georgia Natural Areas Act to identify and preserve areas of unusual ecological significance in a natural state. The Shore Protection Act protects sand dunes, beaches, sandbars, and shoals.
Existing bird nesting sites have been posted to keep humans out. Some sites have been restricted to humans altogether. The population of Georgia's coastline, according to the Combined Coastal Management Program, is growing 20 percent every decade. Therefore, to provide a way for humans and animals to live in harmony, a citizens panel's proposal for protecting bird habitats on five coastal islands has called for people to be banned from three of the islands and from parts of two others. The Department of Natural Resources now protects Williamson Island in Chatham County, Egg Island Bar in Macintosh County, Satilla River Marsh Island in Camden County, St. Catherines Island Bar in Liberty County, and Pelican Spit in Glynn County, which together make up less than 1 percent of the Georgia coast. Human activity is banned year-round at Egg Island Bar, Satilla River Marsh Island, and St. Catherines Island Bar. People are banned from parts of Pelican Spit and from the middle of Williamson Island. The off-limits areas are marked with signs and a ribbon of tape.
These islands are protected because they offer unique habitat for migratory and nonmigratory birds. Egg Island Bar is the state's only nesting site for royal terns and gull-billed terns. Pelican Spit, which is owned by the State of Georgia and located off the coast of Little St. Simons, is a nesting site for thousands of pelicans. Human encroachment chases birds away and threatens populations.
How effective are the monitoring, the restrictions, the posting of sites on stabilizing the bird populations migrating to Georgia? Do these things work? St. Catherines Island Bar was closed to humans in the spring of 1998. "I had not seen any least terns on the island since 1982," says Royce Hayes, superintendent of the St. Catherines Island Foundation. "Within one month of closing the bar, least terns were nesting there again."
Besides the state and federal governments working to protect shorebirds, there are efforts to work with private landowners to take responsibility to manage natural resources on private lands. Little St. Simons Island is privately owned. Kevin McIntyre, the island's resource manager, has been monitoring shorebirds for nine years as part of the International Shorebird Survey of sites in the Western Hemisphere. He surveys the nesting sites of shorebirds from April through June and then August through October, three times a month. The Georgia coast is an important landing spot for the red knots, wimbrels, Wilson's plovers, and oystercatchers. Since 1987, there have been 10 to 15 pair colonies that have tried to establish, but no chicks were produced.
"There seems to be a certain threshold of numbers in a colony to defend against predators for the colony to survive," says McIntyre. To insure shorebird survival, McIntyre supports visitor management programs. Visitor management means informing people who visit Little St. Simons Island of what happens when people invade colonies and the birds are pulled off the nests. Birds are beautiful and interesting; people want to watch them. However, in the summer with temperatures of 95 degrees Fahrenheit, eggs are on the hot sand. If the birds fly up off the nest to mob the visitor, the eggs will overheat and cook in the sand. Therefore, people should stay well below the high tide mark and abide by the postings of nesting sites. If a bird is squawking, a human or predator is invading its territory. Dogs running freely on the beach can disturb a nest.
The nesting sites of least terns are changing. There are no public beach areas in Georgia where the birds are nesting. There is a small spit at the south end of Sea Island where there is little human traffic, and a few pairs of least terns have been counted. Seventy percent of Georgia's surviving least tern pairs are nesting on artificial sites, either dredge sites or rooftops. Nearly 100 percent of Florida's least tern population is on artificial sites. The least tern population in North Carolina and Virginia nesting in artificial sites is increasing.
Volunteer docent programs are being created to offer visitor management at the dwindling number of natural nesting sites of least terns. Information officers who are students working with Ruth Beck of William and Mary College, spoke to 284 people during the Memorial Day weekend at a nesting site for least terns in Virginia. Least terns have been recorded on the site since 1886. The population of the birds at this site has been decreasing at 2.9 percent per year. Beck has monitored this site for seven years. The site is a high-use area for humans. The docent program enables the humans and the birds to occupy the beach together.
To protect the least tern's habitat, a site must be monitored. Data can be gathered to provide information on how many birds, the timing of migration, and if any changes are happening. State agencies and organizations will count the birds and perform surveys, but university researchers carry the monitoring of the birds another step by observing their population and their productivity as they change from the natural sites to the rooftops. Schweitzer monitors six sites from Brunswick to Savannah. Two of the sites are natural, two are dredge sites, and two are rooftop sites.
Some of the monitoring has included using different color dyes to identify the birds. Yellow was used for rooftop birds, blue for beach site birds, and black for dredge site birds. The problem with using dye, though, is that the dye washes off when the birds dive into salty ocean waters. Monitors have been used. Small radio transmitters have been attached to the birds, but the transmitters must be 3 percent of the body weight to keep the birds from losing their equilibrium. Taking this into consideration, these small transmitters must be 0.6 or 0.5 of a gram in weight. With the transmitter so small, the range is small, according to Schweitzer. Plus the transmitters do seem to change the equilibrium of the birds. Least terns have been observed picking the monitors off, carrying them out to sea, and dropping them in the ocean. At $150 each, the transmitters are not practical for monitoring the least terns. In addition, one of the least tern's predators, the crow, is quite adept at learning how nests are marked for monitoring and preying upon the eggs and chicks.
Least terns are opportunists, exploiting the best habi-tats at the optimum times. They appear to be able to adapt, to move from beach, to dredge site, to rooftop. Dredge sites have been used by least terns for nesting sites when the dredge site mimics the beach. These dredge sites get hot but have better wind circulation and water conditions than the rooftop sties.
Dredging in coastal Georgia is performed by the U.S. Army Corps of Engineers to maintain shipping channels at safe operating depths, including the Savannah Harbor, the Port of Brunswick, and the Atlantic Intracoastal Waterway. Material is scooped out of the channel and deposited in designated sites. The dredged material is a combination of river sediment, sand, and shells. The sites are used by the least terns for the first year and possibly the second year. After the first year, the site undergoes changes. Grasses and shrubs appear. The least tern uses a flat, barren land-scape to nest and does not like vegetation. If the site is not maintained, the birds will not return to the dredged site on the third year.
Mike Harris, a wildlife biologist with the Georgia Department of Natural Resources, says that to manage dredge sites, the pile of sand must be pumped up artificially with a tractor. A dredge site in Brunswick is one of the most enduring ones. For 10 years, the U.S. Fish and Wildlife Service and the Corps of Engineers have been maintaining the site for least terns.
Least terns are also moving to rooftops. The roofs attracting the birds are flat, graveled rooftops that mimic the isolated beaches the least terns require. Mike Harris says that Atlantic least terns were first recorded living on rooftops in the 1970s. Tom Murphy, a biologist with the South Carolina Department of Natural Resources, documented least terns on roofs in Charleston in 1970. One rooftop site, monitored by Schweitzer, is located on an industrial building at the Savannah airport; another is located on a manufacturing plant in Savannah. Mike Chapman, a member of the Audubon Society in Brunswick, Georgia, has participated in migration counts of birds for 8 years. At Kings Bay Naval Base in Camden County near St. Marys, Georgia, he discovered least terns nesting on a warehouse roof. The Navy cooperated and closed access to the roof. Some of the personnel even built shade structures, wooden frames 6 inches off the ground with military shading material, the camouflage with slits cut in it to aid in air circulation, to shield the young chicks from the hot sun bouncing off the roof.
Other rooftop nesting sites include a building at the Federal Law Enforcement Training Center and the Glynn Place Mall, both in Brunswick. Schweitzer, who has been monitoring the Atlantic least terns since 1995, has found rooftop colonies on three Savannah-based manufacturing plants.
There are problems with the birds nesting on the roofs. The 150-degree rooftop temperatures bake the eggs and chicks. Other chicks tumble off the rooftop. Eggs are damaged when the adult birds leave the nest. According to Schweitzer, the least tern is clumsy when it flies off. It will push off the nest with its body. The hard, pebble stone roofs, unlike sand on the beach, have no give when the birds put body pressure on the eggs. The eggs are crushed. Now there is an additional problem with the rooftop nesting sites, particularly after Hurricane Hugo. Coastal buildings damaged in the storm have had their pebble stone roofs replaced with smooth, plastic roofs. These replacements were cheaper to install; however, the least terns will not nest on the smooth roofs.
Efforts are being made to stabilize the least tern population and to protect the birds' new rooftop nesting sites. There is not enough information as to whether or not the birds would adapt to yet another type of site; therefore, biologists and ecologists are asking building contractors in the coastal area to consider roofs that would attract least terns. Contractors are being encouraged to use gravel roofs with parapets or edging at least 3, and preferably 12 inches high, as well as screened drains and rain spouts that prevent chicks and eggs from washing off the roof. Building owners are also encouraged not to perform roof repairs during the nesting season when least terns could be disturbed.
The manager of the Glynn Place Mall with rooftop nests has taken his responsibility to the birds seriously. He placed rocks near the nests to mark them and kept maintenance workers away during the nesting season.
Reaction by the public as to how shorebird populations are being monitored, nurtured, and protected has been mixed. Beach conservation is a thorny issue with people reacting in many ways. Some people are sympathetic and understand that we do not know everything about how humans and animals live together but must take time to learn. Other people are outraged that they are restricted from areas where "my grandfather came when he was a boy." Other people vandalize the sites. A pyramid of 96 eggs was formed at one site of least terns, and all the eggs were damaged.
Biologists may have naively thought that the reasons for closing sandbars to humans to protect the birds were common knowledge. Informing the public and educating people as to the importance of maintaining life cycles of birds may lessen some of the tensions among those of us who want to use the beach. Information may provide us with answers to why certain populations change and decline. The message is repeated among the many who watch the birds, who watch the least terns. "If any one species is lost, you're losing diversity and diversity is important in the total picture of our environment," says Ruth Beck.
Life cycles of birds are important to understanding the life cycles of our globe. By putting the pieces together, we may have a better idea of how our human lives will be affected by environmental changes. "Since we don't know how things work," says Mike Harris, "we need to maintain all the parts."
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