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DNR News

Oct. 28, 2013

Results from 2013 Wood Stork Surveys and Nest Monitoring

The federally endangered wood stork (Mycteria americana) nested successfully in South Carolina during 2013. The United States breeding population of wood storks was listed as endangered after nesting pairs declined from between 15,000 and 20,000 in the 1930's to 2,500 pairs by 1978. Historically, wood storks used South Carolina as a feeding area during the summer and fall after dispersing from nesting colonies in Florida and Georgia. In 1981, the first successful wood stork nests were documented in South Carolina (11 nests). Since 1995, wood storks have built between 800–2,060 nests in South Carolina each year.

The S.C. Department of Natural Resources (DNR) counted 2,020 wood stork nests in South Carolina this year. The number of stork nests was down slightly from the record high of 2,057 nests that were counted during 2004. Wood stork nests were observed in 21 colonies in South Carolina this year, including 2 colonies where storks were not known to nest in the past. Aerial surveys were used to locate the nesting colonies. Stork nests were counted during ground surveys or, when ground surveys were not possible, from photographs taken during aerial surveys. During 2013, storks nested in the following counties: Charleston (6 colonies), Beaufort (5 colonies), Colleton (3 colonies), Georgetown (2 colonies), Horry (2 colonies), Hampton (1 colony), Berkeley (1 colony), and Jasper (1 colony).

Favorable weather conditions for storks include a wet season (fall and winter) prior to the onset of nestingWood stork followed by dryer conditions during the nesting season. Storks typically nest in trees growing in water or on small islands. Alligators living below the stork nests deter raccoons and other animals from preying upon the stork eggs and chicks. In addition to requiring water in the colonies for protection, rain during the months leading up to the nesting season increases the amount of fish and other food that is available to nesting storks.

Unlike herons and egrets, which hunt visually, wood storks are tactile feeders, which means that they hunt by feeling for fish, crustaceans, and other prey. This feeding strategy requires high concentrations of prey in water that is shallow enough for storks to wade. When natural and impounded wetlands with abundant fish slowly dry out, excellent feeding conditions are created for the storks. In order for the storks to nest successfully, prey must be abundant and available throughout their nesting season. When adequate food is not available, adult wood storks will abandon their chicks and leave the area to find food.

During 2011, DNR began to monitor individual stork nests in a few index colonies to determine how successful the storks are at raising young in South Carolina. This year, DNR staff, USFWS staff, and four dedicated volunteers monitored nests at nine colonies located between Hilton Head and Charleston. Two of the colonies are on land managed by DNR (Donnelley Wildlife Management Area and Dungannon Plantation Heritage Preserve ), and the other seven colonies are on private land. Nests were mapped when the storks started incubating eggs and monitored from a distance until the chicks reached fledging age (mature enough to fly, which is about 8 weeks after hatching). The average number of chicks survived to fledging age per nest was determined for each colony.

A brief period of unseasonably cold weather in late March caused storks to abandon nests built early in the season. It appeared that many storks returned and nested again once temperatures increased. In June, Tropical Storm Andrea resulted in the loss of some stork chicks, but most of the chicks survived the storm. The 2013 nesting season was longer and less synchronous than usual. Some chicks did not fledge until the first week of September.

This year, a total of 426 stork nests were monitored in seven colonies, and an average of 1.4 chicks fledged per nest site. Chick survival rates were higher during 2013 compared to 2012, when an average of 1.1 chicks fledged in the nests that were monitored (312 nests, 7 colonies). The federal recovery goal for wood storks is an average of 1.5 fledglings per nest. Fluctuations in the number and success of nests among years are normal.
An aerial survey was conducted in late June to determine if storks reproduced successfully at the colonies where nests were not monitored. The storks appeared to have had a successful season at 16 colonies, but failed to fledge a significant number of chicks at 5 colonies. Potential causes of colony failure for wood storks include predation, inadequate food during the chick rearing period, and disturbance. Storks nested successfully at eight of the nine index colonies that were monitored this year, but an average of 34% of the monitored nest sites failed to produce any fledglings. Mammalian predators are believed to be the cause of failure at the unsuccessful colony that was monitored.


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