|Colonial Nesting Wading Birds
Black-crowned Night Heron Nycticorax nycticorax
Glossy Ibis Plegadis falcinellus
Great Blue Heron Ardea herodias
Great Egret Casmerodius albus
Green Heron Butorides virescens
Little Blue Heron Egretta caerulea
Reddish Egret Egretta rufescens
Roseate Spoonbill Platalea ajaja
Snowy Egret Egretta thula
Tricolored Heron Egretta tricolor
White Ibis Eudocimus albus
Wood Stork Mycteria americana (described in more detail in separate account)
Yellow-crowned Night Heron Nyctanassa violacea
Contributors (2005): Elizabeth A. Ciuzio and Thomas M. Murphy
Reviewed & Edited (2012): Christine E. Hand
Photo of White Ibis by SC DNR
Taxonomy and Basic Description
As the name suggests, colonial nesting wading birds nest in aggregations called colonies and feed by capturing prey while wading through or standing in shallow water. Colonial nesting wading birds are a taxonomically diverse group. Members of this guild belong to two orders: Pelecaniformes and Ciconiiformes. Pelecaniformes includes three families: Ardeidae (herons, bitterns and egrets), Threskiornithidae (ibises and spoonbills) and Pelecanidae (pelicans). Ciconiiformes includes one family: Ciconiidae (storks). Prior to the reclassification that occurred during 2010, all wading birds were classified as Ciconiiformes. Wading birds are medium to large birds that have long legs, necks and bills. Males and females look similar to each other. Immature birds often have different plumages than adults. These species typically nest and feed in wetland habitats. Cattle egrets (Bubulcus ibis) are also in the Ardeidae family but are not included in this account because they are not a true wetland species.
Wading birds are among the most striking birds in North America. The white ibis, great egret, snowy egret and wood stork are predominantly white birds. These four species are easily distinguished from each other by size and by the color of their wing feathers, bills and legs. The white ibis has a scarlet bill and legs and black wing tips. The snowy egret has dark legs with yellow feet. The great egret is tall with a yellow bill and black legs, and the wood stork is very large with a black neck, head, legs, and wing feathers.
Photo of Snowy Egret by SC DNR
reat blue, little blue, green and tricolored herons as well as the night herons appear as their names suggest. The great blue is predominantly bluish gray and has white on the crown, cheeks and a stripe down the neck. The little blue heron is a darker blue and considerably smaller than the great blue heron. Little blue heron chicks are white when they hatch and immature birds are white. The tricolored heron is slate blue above and on the neck, with a white abdomen and white stripe on the front of the neck. The green heron is small and compact with a relatively short neck and legs. They have a greenish black cap, dark grayish back and wings, reddish neck, and gray under-parts. The yellow-crowned night heron is overall a grayish bird with yellow on the crown and white on its head and cheeks. The black-crowned night heron is also a grayish bird with black on its crown and down its back.
The glossy ibis appears to be an all dark bird from a distance. Upon closer inspection, the glossy ibis is actually a glossy chestnut color. Reddish egrets have two color morphs: white and dark. A small number of dark morph reddish egrets are known to breed in South Carolina. Their appearance is similar to little blue herons, but their necks are more reddish, their bills have a pink base, and they are typically found at the coast. The roseate spoonbill has pink plumage and a spoon-shaped bill. As of 2011, spoonbills have not been found nesting in South Carolina, but they are regularly observed in the state.
The terminology used to describe wading birds can be confusing. In North America, the term “wading bird” is used to refer to storks, herons, and egrets. In other areas of the world, shorebirds such as oystercatchers and sandpipers are often referred to as wading birds. The sites where groups of wading birds nest are referred to as colonies or rookeries. Sites where groups of wading birds rest during the day or overnight are called roosts and groups of feeding wading birds are referred to as flocks or feeding aggregations.
Members of this guild are of conservation concern because their reproductive strategy leaves them especially vulnerable to habitat degradation. Many wading bird species nest in large colonies; dozens of birds can nest in a single tree. Although this strategy affords benefits in terms of predator avoidance, it makes them especially vulnerable to habitat loss because the degradation of a small area (colony) can affect hundreds of breeding pairs of several different species. Food availability may be the limiting factor for many colonies in South Carolina. The loss of feeding habitat near a colony site can make the colony unsuitable even if the colony site itself is unaltered.
In addition to this vulnerability to habitat alterations, several members of this guild are of special concern due to declining population trends (Sauer et al. 2011). With the exception of the great blue heron, all of the colonial wading bird species have been in decline in recent years in South Carolina. The roseate spoonbill is listed as a Bird of Conservation Concern in the Southeastern Coastal Plain, and the little blue heron, black-crowned night heron, snowy egret and reddish egret are listed for other regions of the United States (USFWS 2008). The North American Waterbird Conservation Plan (Waterbird Conservation for the Americas) listed the little blue heron, snowy egret, tricolored heron and wood stork as species of high concern, and the black-crowned night heron, reddish egret, roseate spoonbill, white ibis, and yellow-crowned night heron as species of moderate concern (Kushlan et al. 2002). The glossy ibis and green heron were listed as species of low concern, and the cattle egret and great egret were listed as not currently at risk (Kushlan et al. 2002).
POPULATION DISTRIBUTION AND SIZE
All of the colonial nesting wading birds can be found in the coastal zone of South Carolina. The glossy ibis, tricolored heron, reddish egret and snowy egret are restricted to the coastal zone, while the great egret, little blue heron and white ibis can range into the coastal plain. The yellow-crowned night heron is an uncommon breeder in the piedmont (Post and Gauthreaux 1989). The black-crowned night heron is a coastal breeder, is uncommon in the coastal plain away from coast and is not found in sandhills, piedmont or mountains. The great blue heron can be found throughout the state.
Complete ground censuses of nests in wading bird colonies in the coastal plain and coastal zone were conducted in 1988, 1989, 1994 and 1996. Counts of the total number of wading bird nests fluctuated among years, but high counts of 59,483 and 52,587 in 1989 and 1996 were representative of the population (Dodd and Murphy 1997). The fluctuations were primarily a result of one species: white ibis. Nesting populations of members of this guild appeared to be stable between 1988 and 1996.
Since that time, aerial estimates indicate the number of wading birds nesting in South Carolina has declined precipitously. This was particularly apparent during years of extended drought from 1999 through 2003. Although rainfall has returned to near normal levels, there has not been a return to historic nest numbers.
HABITAT AND NATURAL COMMUNITY REQUIREMENTS
Nesting sites are found in a variety of habitats. Colony sites for most guild members are found on islands in fresh and brackish water ponds. Water surrounding a nesting site deters mammalian predators and alligators frequently provide an additional deterrent. When suitable island sites are lacking, guild members may use vegetation around the edge of a pond for nesting. These sites are generally unsuccessful as a result of predation except for ponds in residential areas that are not affected by predators. Colonies are also sustained on estuarine islands that are free of mammalian predators. Larger species such as wood storks and great egrets prefer mature trees with large lateral limb structures. Smaller species such as night herons, little blue herons, tricolored herons and snowy egrets nest lower and prefer shrubby habitat.
Great blue herons nest in mature pines on hammocks islands, along the marsh-upland ecotone or in riparian swamps. Further away from the coast, they nest on islands or along the riparian zone of rivers and man-made water bodies, such as reservoirs.
Wading birds feed primarily on fish, crabs, crayfish, insects and amphibians and can be found feeding in a wide variety of aquatic habitats. Some species also feed opportunistically on small birds and mammals. Gradually receding water levels concentrate prey and facilitate feeding.
Each species has its own feeding style. Ibises, storks and spoonbills have specialized sensitive bills and are tactile feeders, which means that they use touch to locate prey. They require high prey densities in shallow water to feed efficiently. These species can feed in even when visibility is low, such as in murky water and at night. They can feed efficiently in large groups even when the water is stirred up, which allows them to take advantage of ephemeral food sources. The glossy and white ibises use their long bills to probe for invertebrates in moist soil and shallow water. Wood storks and roseate spoonbills wade through shallow water while sweeping their bills back and forth through the water to locate and capture prey. When their lower bill comes into contact with a fish, the stork reflexively snaps its bill shut to capture the prey. Storks also pump their feet while feeding to startle prey.
Most egrets and herons are visual hunters, which means that they locate prey visually before striking. They can capture a variety of types of prey in various situations but cannot forage efficiently when visibility is poor. These species perch at the edge of the water or wade out into shallow water to search for prey. The great blue heron and great egret are able to tolerate deeper water owing to their long legs. Snowy egrets and reddish egrets are very active feeders and purse their prey while great egrets and great blue herons are “lie-in-wait” predators.
Loss of feeding, roosting and breeding habitat is the biggest problem for colonial wading birds (Dodd and Murphy 1998). Over 50% of the wetlands in the contiguous United States were drained or converted to other uses between 1780s and 1980s (Dahl 1990). Since the 1970s, the rate of wetland loss in the United States has been greatest in the southeastern. While South Carolina has been relatively successful in protecting its wetland significant losses have occurred in freshwater non-tidal wetlands. The amount and quality of foraging habitat will ultimately determine the status of colonial wading bird populations.
Suitable nesting and roosting habitat is reduced by removal of vegetation during timber harvest and residential and commercial development. Shrub-type nesting and roosting habitat is lost through removal of vegetation, mainly for aesthetic reasons, along the edge of ponds and impoundments. Competition with cattle egrets (Bubulcus ibis) and double-crested cormorants (Phalacrocorax auritus) for food resources and nesting sites can reduce nesting success for guild members (USFWS 2003).
Human disturbance is a problem for nesting colonial wading birds. Short-term disturbances such as airplanes, boats, vehicles and human presence may cause the birds to fly from their nests, which can result in nest abandonment. Unattended eggs and chicks are vulnerable to depredation and to overheating. Disturbance at feeding areas can reduce the amount of prey that wading birds are able to consume and to feed to their young. Docks result in disturbance to feeding birds because of the increased boat traffic. The docks themselves are frequently used by the birds for foraging because fish concentrate in the shade of the docks.
Several types of environmental contaminants are problems for colonial wading birds. Petroleum from oil spills damages bird feathers and causes mortality. Chemicals such as DDT and PCBs are not currently widespread; however they do cause reduced reproductive success. Metals such as mercury and lead can concentrate and lead to reduced survivorship and reproductive success. Environmental contaminants also reduce availability of prey items. Nonpoint sources of pollution can reduce productivity of coastal marshes. Diseases such as cholera and botulism are particularly problematic for colonial wading birds. In the event of an outbreak of these diseases, they spread easily because the birds nest in such high densities.
Other human-related causes of mortality include collisions with power lines and entanglement in fishing line, gill nets, drift nets and various forms of plastics (Dodd and Murphy 1998).
The Lacey Act of 1900 was the first major step toward protecting wading birds. The Lacey Act was passed, in part, in response to the millinery trade to regulate interstate and international trade of bird parts. Hundreds of thousands of herons and egrets, among other birds, were killed for their nuptial plumes, used in ladies hats and fashionable clothing (Ogden 1978).
The Migratory Bird Treaty Act of 1918 made it illegal for a person to possess any migratory bird or part, with the exception of game birds during the proper season, as well as the possession of nests and eggs. Prior to these Acts, market hunting was responsible for population declines in many bird species.
The South Carolina Department of Natural Resources (SCDNR) collected baseline data during statewide ground census counts were 1988, 1989, 1994 and 1996. Statewide aerial surveys have been conducted annually since 1988, with the exception of 2009 and 2010, when SCDNR did not employee a wading bird biologist.
Conduct Research and Inform Permitting Agencies
Annually survey colonies containing federally endangered birds.
Complete a statewide ground census of nesting wading birds for two consecutive years at least every ten years OR develop an alternative plan for monitoring population trends that incorporates aerial and ground surveys of a subset of the colonies in the state.
Coordinate with biologists in Southeastern Coastal Plain to develop plans to monitor wading birds on a regional scale.
Monitor individual nests at a subset of colonies to determine productivity.
Identify important foraging areas near nesting colonies and determine how far from the colonies different species travel to forage.
Determine the effects of human activity on wading bird foraging efficiencies, and the importance of roost sites and their relationship to available foraging habitat.
Partner with Industry, Developers, and Private Property Owners/Managers to Protect Nesting and Feeding Habitat
Provide technical and/or financial assistance to property owners for projects that will significantly benefit wading bird conservation.
Determine Best Management Practices for multi-species management of impounded marsh habitat. Integrate management for colonial wading birds into traditional waterfowl management of currently impounded wetlands by timing draw downs during key feeding periods (post fledging).
Partner with industry and permitting agencies to prevent the destruction of important wading bird breeding, feeding and roosting sites.
Determine and encourage the use of Best Management Practices for residential and commercial development activities near nesting and feeding sites.
Maintain vegetated visual buffers around nesting colonies and feeding areas to protect birds from human disturbance.
Include islands with suitable nesting habitat when constructing new ponds.
Leave shrubs around the edges of ponds to provide nesting and foraging habitat and for bank stabilization.
Minimize fertilizer, herbicide, and pesticide runoff into wetlands.
Document water quality issues at colony sites and partner with appropriate permitting agency to reduce input of chemical contaminants and untreated wastewater into wetlands.
Place landfills, power lines and towers away from colonies and wetland areas.
Acquire, or assist conservation organizations to acquire, and manage important nesting and feeding sites to benefit wading birds.
Support Outreach and Public Education
Provide information about wading birds in South Carolina to the public via the SCDNR website and news releases.
Provide opportunities for the public to view and appreciate wading birds while preventing disturbance to nesting and foraging birds.
Install educational kiosks and signs at sites where the public can view wading birds.
MEASURES OF SUCCESS
Protecting important habitat as outlined above should provide stable resources and enable populations to rebound. Wading bird nesting colonies should be distributed widely across coastal plain counties. The ultimate measure of success would be to document stable to increasing population trends of colonial wading birds.
Dahl, T. E. 1990. Wetlands losses in the United States 1780's to 1980's. U.S. Department of the
Interior, Fish and Wildlife Service, Washington, D.C. Jamestown, ND: Northern Prairie Wildlife Research Center Online. (Version 16JUL97). Accessed on November 4, 2011 at http://www.npwrc.usgs.gov/resource/wetlands/wetloss/index.htm.
Dodd, M.G. and T.M. Murphy. 1997. The status and distribution of wading birds in South Carolina, 1988–1996. South Carolina Department of Natural Resources SG9610-A. Columbia, South Carolina.
Dodd, M.G. and T.M. Murphy. 1998. Colonial wading birds in the Charleston harbor estuary. The Charleston Harbor Project. South Carolina Department of Natural Resources. Columbia, South Carolina.
Ogden, J.C. 1978. Population trends of colonial wading birds on the Atlantic and Gulf coasts. Pp. 137–153. In: Wading birds, A. Sprunt IV, J.C. Ogden and S. Winckler, Eds. New York, New York.
Kushlan, J.A., M.J. Steinkamp, K.C. Parsons, J. Capp, M. Acosta Cruz, M. Coulter, I. Davidson,
L. Dickson, N. Edelson, R. Elliot, R.M. Erwin, S. Hatch, S. Kress, R. Milko, S. Miller, K.
Mills, R. Paul, R. Phillips, J.E. Saliva , B. Sydeman, J. Trapp, J. Wheeler, and K. Wohl.
2002. Waterbird Conservation for the Americas: The North American Waterbird
Conservation Plan, Version 1. Waterbird Conservation for the Americas, Washington,
DC, U.S.A ., 78 pp.
Post, W. and S.A. Gauthreaux, Jr. 1989. Status and abundance of South Carolina birds. Cont. Charleston Museum XVIII. Charleston, South Carolina. 83 pp.
Sauer, J. R., J. E. Hines, J. E. Fallon, K. L. Pardieck, D. J. Ziolkowski, Jr., and W. A. Link. 2011. The North American Breeding Bird Survey, Results and Analysis 1966 - 2009. Version 3.23.2011 USGS Patuxent Wildlife Research Center, Laurel, MD
United States Fish and Wildlife Service. 2003. Final Environmental Impact Statement: Double-crested Cormorant Management in the United States. Division of Migratory Bird Management. Arlington, Virginia. 139 pp. Accessed on October 18, 2011 at http://library.fws.gov/Bird_Publications/CormorantFEIS.pdf.
United States Fish and Wildlife Service. 2008. Birds of conservation concern 2008. Division of Migratory Bird Management. Arlington, Virginia. 85 pp. Accessed on October, 18, 2011 at http://library.fws.gov/bird_publications/bcc2008.pdf.