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Mycteria americana

(American Wood Stork)

Overview

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Wood storks are large wading birds approximately 3 1/2 feet in height with a wing span of over 5 feet. They are distinguished by a dark unfeathered head and neck, a white body, and a black tail and wing tips . Like most other wading birds, wood storks feed on small fish in shallow freshwater wetlands. They use tall cypresses near the water for colonial nest sites.

Wood storks (Mycteria americana) are one of two species of storks that breed in North America. This large, long-legged inhabitant of marshes, cypress swamps , and mangrove swamps reaches the northern limit of its breeding range in the southeastern U.S., where it breeds in colonies with great egrets, snowy egrets, white ibises, and many other species. The unique feeding method of the wood stork gives it specialized habitat requirements; the habitats on which wood storks depend have been disrupted by changes in the distribution, timing, and quantity of water flows in South Florida. The population declines that accompanied this disruption led to its listing as an endangered species and continue to threaten the recovery of this species in the U.S.

Endangered
Threat status

Common Names

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Click on the language to view common names.

Common Names in Czech:

Nesyt Americký

Common Names in Danish:

Amerikansk Skovstork

Common Names in Dutch:

Kaalkopooievaar

Common Names in English:

American Jabiru, American Wood Ibis, American Wood Stork, Flinthead, Gannet, Gourdhead, Hammerhead, Ironhead, Preacher, Spanish Buzzard, Wood Ibis, Wood Stork

Common Names in Estonian:

Muda-Toonekurg

Common Names in Finnish:

Amerikaniibishaikara

Common Names in French:

Cigogne Américaine, Tantale D'amërique, Tantale D'amérique

Common Names in German:

Amerikanischer Nimmersatt, Waldstorch

Common Names in Guarani:

Tujuju Kangy

Common Names in Haitian Creole Frenc:

Tantal Rak Bwa

Common Names in Italian:

Cicogna Americana, Tantalo Americano

Common Names in Japanese:

Amerikatokikou, アメリカトキコウ

Common Names in Latin:

Mycteria americana

Common Names in Norwegian:

Amerikastork

Common Names in Polish:

Dlawigad Amerykanski

Common Names in Portuguese:

Cabeça-De-Pedra, Cabeça-Seca

Common Names in Portuguese (Brazil):

Cabeça Seca, Cabeça-Seca

Common Names in Russian:

ÐиÑÑ‚ леÑной, американÑкий клювач

Common Names in Slovak:

Bocian Lesný

Common Names in Spanish:

Cayama, Cigüeña Americana, Tántalo Americano

Common Names in Spanish (Argentine):

Tuyuyú

Common Names in Spanish (Bolivia):

Tuyuyú

Common Names in Spanish (Costa Rica):

Cigueñón

Common Names in Spanish (Cuba):

Cayama

Common Names in Spanish (Dominican R:

Coco

Common Names in Spanish (Honduras):

Cigüeña

Common Names in Spanish (Mexico):

Cigueña Americana

Common Names in Spanish (Nicaragua):

Cigüeña Americana

Common Names in Spanish (Paraguay):

Tuyuyú

Common Names in Spanish (Uruguay):

Cigüeña Cabeza Pelada

Common Names in Swedish:

Amerikansk Ibisstork

Common Names in unspecified:

Wood Stork

Description

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Family Ciconiidae

Large, long-legged, long-necked wading birds with long stout bills. Only 19 living species, they are all mute.

Physical Description

Adult : Head : bare, dirty brownish-black Bill: blackish Curvature: decurved Length : long Shape : thick heavy bill drooped at tip Neck: bare, dirty brownish-black Body: white Legs : Foot Color: blackish Leg Color: blackish gray Wings: Flight Feathers: black Secondaries: black Tail: black.Immature: Head: grayish down Bill: horn color or yellowish Curvature: decurved Length: long Shape: thick heavy bill drooped at tip Neck: grayish down Body: dull white Legs: Foot Color: blackish Leg Color: blackish gray Wings: Secondaries: black.

Color:

White body. Black tail, legs , and flight feathers.

Adult : Dark bill

Immature : Yellow bill · Feathered head is grayish-brown

Size/Age/Growth

About 35 to 45 inches long, with a wingspan of 65 to 65 inches. Adults weigh about 96 ounces .

Habitat

The wood stork is primarily associated with freshwater and estuarine habitats for nesting, roosting, and foraging . Wood storks typically construct their nests in medium to tall trees that occur in stands located either in swamps or on islands surrounded by relatively broad expanses of open water (Palmer 1962, Rodgers et al. 1996, Ogden 1991). Historically, wood storks in South Florida established breeding colonies primarily in large stands of bald cypress (Taxodium distichum) and red mangrove (Rhizophora mangle). The large, historic Everglades NP nesting colonies were in estuarine zones. These estuarine zones are also an important feeding habitat for the nesting birds. In one study of wood stork nesting throughout Florida, which was conducted prior to the 1960s, more than half of all wood stork nests were located in large bald cypress stands, 13 percent were located in red mangrove, eight percent in partially harvested bald cypress stands, six percent in dead oaks (Quercus spp. ), and five percent in small pond cypress (T. distichum var. nutans) (Palmer 1962). Wood storks have also been observed constructing their nests in custard (pond) apple (Annona glabra), black gum (Nyssa biflora), buttonwood (Conocarpus erectus), black mangrove (Avicenna germinans), strangler fig (Ficus aurea), and southern willow (Salix carolina). Coastal nest sites occur in red mangroves and, occasionally, Brazilian pepper (Schinus terebinthifolius), cactus (Opuntia stricta), and Australian pine (Casuarina equisetifolia).

During the nonbreeding season or while foraging, wood storks occur in a wide variety of wetland habitats. Typical foraging sites for the wood stork include freshwater marshes and stock ponds , shallow, seasonally flooded roadside or agricultural ditches, narrow tidal creeks or shallow tidal pools, managed impoundments , and depressions in cypress heads and swamp sloughs. Because of their specialized feeding behavior, wood storks forage most effectively in shallow-water areas with highly concentrated prey (Ogden et al. 1978, Browder 1984, Coulter 1987). In South Florida, low, dry-season water levels are often necessary to concentrate fish to densities suitable for effective foraging by wood storks (Kahl 1964, Kushlan et al. 1975). As a result, wood storks will forage in many different shallow wetland depressions where fish become concentrated, either due to local reproduction by fishes , or as a consequence of seasonal drying.

The loss or degradation of wetlands in central and South Florida is one of the principal threats to the wood stork. Nearly half of the Everglades has been drained for agriculture and urban development (Davis and Ogden 1994). The Everglades Agricultural Area (EAA) alone eliminated 802,900 ha of the original Everglades, and the urban areas in Miami-Dade, Broward and Palm Beach counties have contributed to the loss of spatial extent of wood stork habitat. Everglades NP has preserved only about one-fifth of the original extent of the Everglades, and areas of remaining marsh outside of the Everglades NP have been dissected into impoundments of varying depths.

The U.S. Army Corps of Engineers’ (COE) Central and Southern Florida (C and SF) Project encompasses 4,660,000 ha from Orlando to Florida Bay and includes about 1,600 km each of canals and levees , 150 water control structures, and 16 major pump stations . This system has disrupted the volume, timing, and direction of fresh water flowing through the Everglades. The natural sheet flow pattern under which the Everglades evolved since about 5,000 years ago has not existed for about 75 years (Leach et al. 1972, Klein et al. 1974). The diversion of natural sheet flow to canals, the loss of fresh water to seepage and to pumping to tidal waters, and the extraction of fresh water for irrigation and urban water supply has led to saltwater intrusion in coastal counties from St . Lucie County on the east coast to Sarasota County on the west coast.

Although the major drainage works completed the conversion of wetlands to agriculture in the EAA by about 1963, loss of wetlands continues to the present at a slower, but significant rate. In the entire State of Florida between the mid-1970s to the mid-1980s, 105,000 ha of wetlands (including marine and estuarine offshore habitats) were lost; we do not have an estimate for freshwater wetlands in central and south Florida (Hefner et al. 1994).

Vegetation: freshwater marshes, saltwater and brackish marshes, freshwater lakes and ponds • Maximum Elevation: 800 meters • Foraging Strata: Water • Center of Abundance: Lower tropical: lowlands, lower than 500 m.; tropics. • Sensitivity to Disturbancet: Low

Typically found in the intertidal zone at the water's edge at a mean distance from sea level of 275 meters (903 feet).[1]

Ecology: List of Habitats : 5.4 Wetlands (inland) - Bogs , Marshes, Swamps , Fens , Peatlands 5.5 Wetlands (inland) - Permanent Freshwater Lakes (over 8ha) 12.5 Marine Intertidal - Salt Marshes (Emergent Grasses)

Biology

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Diet

Wood storks use a specialized feeding behavior called tactolocation, or grope feeding. A foraging wood stork wades through the water with its beak immersed and partially open (7 to 8 cm). When it touches a prey item, a wood stork snaps its mandibles shut, raises its head , and swallows what it has caught (Kahl 1964). Regularly, storks will stir the water with their feet, a behavior which appears to startle hiding prey (Rand 1956, Kahl 1964, Kushlan 1979). Tactolocation allows storks to feed at night and use water that is turbid or densely vegetated. However, the prey must be concentrated in relatively high densities for wood storks to forage effectively. The natural hydrologic regime in South Florida involves seasonal flooding of extensive areas of the flat, low-lying peninsula, followed by drying events which confine water to ponds and sloughs . Fish populations reach high numbers during the wet season , but become concentrated into smaller areas as drying occurs. Consumers , such as the wood stork, are able to exploit high concentrations of fish in drying pools and sloughs. In the pre-drainage Everglades , the dry season of South Florida provided wood storks with ideal foraging conditions by concentrating prey species in gator holes and other drainages in the Everglades basin . In coastal areas, the tidal cycle strongly influences use of saltwater habitats by wood storks. The relatively great tidal amplitudes characteristic of coastal marshes in northeast Florida, Georgia, and South Carolina serve to concentrate prey. similarly to the seasonal drawdowns found in freshwater systems (FWS 1997).

Storks forage in a wide variety of shallow wetlands, wherever prey reach high enough densities, and in water that is shallow and open enough for the birds to be successful in their hunting efforts (Ogden et al. 1978, Browder 1984, Coulter 1987). Good feeding conditions usually occur in relatively calm water, where depths are between 10 and 25 cm, and where the water column is uncluttered by dense patches of aquatic vegetation (Coulter and Bryan 1993). In South Florida, dropping water levels are often necessary to concentrate fish to suitable densities (Kahl 1964, Kushlan et al. 1975). In east-central Georgia, where stork prey is almost twice as large as the prey in Florida, wood storks feed where prey densities are significantly lower than foraging sites in Florida (Coulter 1992, Coulter and Bryan 1993, Depkin et al. 1992). Typical foraging sites throughout the wood stork’s range include freshwater marshes and stock ponds , shallow, seasonally flooded roadside or agricultural ditches, narrow tidal creeks or shallow tidal pools, managed impoundments , and depressions in cypress heads and swamp sloughs. Almost any shallow wetland depression that concentrates fish, either through local reproduction or the consequences of area drying, may be used as feeding habitat.

Wood storks feed almost entirely on fish between 2 and 25 cm in length (Kahl 1964, Ogden et al. 1976, Coulter 1987). In South Florida, Ogden et al. (1976) found that certain fish species were taken preferentially. Mosquito fish (Gambusia affinis ) were under represented in the diet in proportion to abundance , whereas, flagfish (Jordanella floridae), sailfin mollies (Poecilia latipinna), marsh killifish (Fundulus confluentus), yellow bullheads (Ictalurus natalis), and sunfish (Centrarchidae) were over represented. Wood storks also occasionally consume crustaceans, amphibians , reptiles , mammals, birds, and arthropods . Fish densities at stork foraging sites varied from 15.6 individuals/m2 in east-central Georgia to 40 individuals/m2 in South Florida (Ogden et al.1978, Depkin et al. 1992).

Because wood storks rely on concentrated food sources which are patchily distributed over large areas, they need to be able to find new feeding grounds with minimal energy expenditure. Wood storks have soaring abilities that allow them to reach high altitudes and many kilometers without the energy expenditure of wing-flapping. A recent study suggested that soaring flight by storks can be accomplished at one-tenth the energetic cost of flapping flight (Bryan and Coulter 1995). The long distances they travel, however, shortens the time available to wood storks for feeding and reduces the number of times an adult stork can return to its nest to feed young (Kahl 1964). During the breeding season , feeding areas proximal to wood stork breeding colonies may play an important role in chick survival and provide enhanced opportunities for newly fledged birds to learn effective feeding skills.

Reproduction

Mating occurs after a period of highly ritualized courtship displays at the nest site (Kahl 1972). As a female bird approaches, male birds establish themselves at potential nest sites and perform ritualized preening behavior. Rival males will extend their necks, grab their opponents’ bills, and clatter their bills loudly a few times. Females respond by bill gaping and a spread-winged balancing posture. Females will be turned away initially, but after repeated approaches, will respond by swaying their heads , preening, or playing with nearby twigs (Kahl 1972). During copulation , males loudly clatter their bills. Mated pairs greet each other with exaggerated, mutual up-down head movements and hissing calls .

Wood storks tend to use the same colony sites over many years, as long as the sites remain undisturbed and sufficient feeding habitat remains in the surrounding wetlands. Site turnover rates for the colonies in South Carolina are very low at 0.17 colonies per year. Current year colonies have an 89 percent likelihood of remaining active in consecutive years. However, many of these South Carolina colonies are relatively recent.

Traditional wetland nesting sites may be abandoned by storks once local or regional drainage schemes remove surface water from beneath the colony trees. Maintaining adequate water levels to protect nests from predation is a critical factor affecting production of a colony. The lowered water levels allow nest access by raccoons and other land-based predators . As a result of such drainages and predation, many storks have shifted colony sites from natural to managed or impounded wetlands. The percentage of wood storks that nested in either altered wetlands (former natural wetlands with impounded water levels) or artificial wetlands (former upland sites with impounded water) in central and north Florida colonies increased from about 10 percent in 1960 to between 60 and 82 percent between 1976 and 1986.

Wood storks are seasonally monogamous, probably forming a new pair bond every season . Three and 4-year-old birds have been documented to breed , but the average age of first breeding is unknown. Once wood storks reach sexual maturity they are assumed to nest every year; there are no data on whether they breed for the remainder of their life or whether the interval between breeding attempts changes as they age (FWS 1997).

Wood storks construct their nests in trees that are usually standing in water or in trees that are on dry land if the land is a small island surrounded by water. The nest are large rigid structures usually found in the forks of large branches or limbs. Storks may add guano to the nest to stabilize the twigs. (Rodgers et al. 1988). The nest may be constructed in branches that are only a meter above the water or in the tops of tall trees. They construct their nests out of sticks , with a lining of finer material . Their nests are flat platforms, up to 1 m in diameter, and are maintained by the adult storks throughout the breeding season . Although both adults maintain the nest, the male wood stork usually brings nest material to the female after they complete their courtship (Palmer 1962).

The date on which wood storks begin nesting varies geographically. In Florida, wood storks lay eggs as early as October and as late as June (Rodgers 1990). In general, earlier nesting occurs in the southern portion of the state (below 27°N). Storks nesting in the Everglades and Big Cypress basins , under pre-drainage conditions (1930s to 1940s), formed colonies between November and January (December in most years) regardless of annual rainfall and water level conditions (Ogden 1994 and 1998). In response to deteriorating habitat conditions in South Florida, wood storks in these two regions have delayed the initiation of nesting, approximately two months, to February or March in most years since the 1970s. This shift in the timing of nesting is believed to be responsible for the increased frequencies of nest failures and colony abandonment in these regions over the last 20 years; colonies that start after January in South Florida risk having young in the nests when May-June rains flood marshes and disperse fish.

Female wood storks lay a single clutch of eggs per breeding season. However, they will lay a second clutch if their nests fail early in the breeding season (M. Coulter 1996). Wood storks lay two to five (usually three) eggs depending on environmental conditions ; presumably larger clutch size in some years are responses to favorable water levels and food resources . Once an egg has been laid in a nest, one member of the breeding pair never leaves the nest unguarded. Both parents are responsible for incubation and foraging (Palmer 1962). Incubation takes approximately 28 days, and begins after the first one or two eggs are laid; therefore egg-hatching is asynchronous.

Younger, smaller chicks are often the first to die during times of food stress (FWS 1997). It takes about 9 weeks for the young to fledge ; once they fledge, the young stay at the nest for an additional 3 to 4 weeks to be fed by their parents. Parents feed the young nestlings by regurgitating whole fish into the bottom of the nest; parents feed the young three to 10 or more times per day. Larger nestlings are fed directly bill to bill. Feedings tend to be more frequent when young are small. Ogden et al. (1978) reported that only one to two feedings per day, per nest, have been recorded in South Florida colonies when adults were forced to fly great distances to locate prey . Kahl (1964) calculated that an average wood stork family (two adults and two nestlings) requires 201 kg (443 lbs ) of fish during a breeding season, and that a colony of 6,000 nests therefore requires 1,206,000 kg of fish during the breeding season. A similar calculation for a typical Everglades NP or Corkscrew Swamp colony with 200 nests would require 40, 200 kg (88,600 lbs) of fish during the breeding season.

The production of wood stork colonies varies considerably between years and locations, apparently in response to differences in food availability; colonies that are limited by food resources may fledge an average of 0.5 to 1.0 young per active nest; colonies that are not limited by food resources may fledge between 2.0 and 3.0 young per active nest (Ogden 1996a).

Migration

Nonmigratory. During the non-breeding season (the summer to fall rainy season in South Florida), juvenile wood storks from South Florida colonies have been located throughout the Florida peninsula, southern Georgia, coastal South Carolina, central Alabama, and east-central Mississippi (Ogden 1996a). Additionally, marked individuals from a colony in east-central Georgia were found in the central Everglades during the winter. This information suggests that the southeastern population of wood storks is a single population that responds to changing environmental conditions through temporal relocation. Rodgers’ (1996) data analysis of genetic variation in wood stork populations in South Florida, central Florida, north Florida, Georgia, and South Carolina support this evaluation.

Taxonomy

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Notes

Name Status: Accepted Name . Latest taxonomic scrutiny: 17-Oct-2001.

Similar Species

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Great Egret, American White Pelican, White Ibis

Members of the genus Mycteria

There are approximately 8 species in this genus:

M. americana (American Wood Stork) · M. cinerea (Milky Stork) · M. cinereus · M. ibis (Yellow-Billed Stork) · M. ibis ibis (Yellow-Billed Stork) · M. leucocephala (Painted Stork) · M. senegalensis · M. wetmorei

More Info

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Further Reading

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Notes

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Contributors

Data Sources

Accessed through GBIF Data Portal March 09, 2008:

Identifiers

Footnotes

  1. Standard Deviation = 876.990 based on 10,598 observations. Terrestrial altitude and ocean depth information for each observation from British Oceanographic Data Centre. [back]
Last Revised: 2009-06-19