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Mycteria americanawood stork

By Sean Carroll

Geographic Range

Mycteria americana range from North America to Argentina. In the United States, wood storks nest in South Carolina, Georgia, and Florida. After breeding they may disperse north to North Carolina or west to Mississippi and Alabama. (Brooks, 2001)

Habitat

Wood storks inhabit mainly tidal waters, marshes, swamps, streams and mangroves. They hunt for prey in shallow, muddy-bottomed banks or wetlands. Their nests are ideally constructed in trees surrounded by water to limit depredation of the eggs. (Brooks, 2001; Ehrlich, et al., 1988)

Physical Description

Adults usually measure one meter tall and can have a wingspan of over one and a half meters. They have a blackish bill, accompanied with a scaly-looking, featherless head and neck which sticks out straight when flying. The majority of the birds' body is white except for the primary, secondary, and tail feathers which are black. Immature wood storks have a pale yellow bill and dull gray-colored head and neck. (Farrand, 1983)

  • Average mass
    2500 g
    88.11 oz
    AnAge
  • Average length
    1 m
    3.28 ft
  • Average wingspan
    1.5 m
    4.92 ft

Development

The eggs are incubated for one month and the newborn chicks hatch weighing only 57 grams. They are completely helpless except for the feathered umbrella that the parents provide with their wings to shield them from heat and rain (Klinkenberg 1998). There is sibling competition for food and under stressful conditions only the first-born and largest will survive. During times of heavy rains, nestlings often die or are deserted by their parents (Ramo and Busto 1992).

Reproduction

Wood storks are monogamous. (Ehrlich, et al., 1988)

Pairs often mate for life and return to the same nest each breeding season to raise their offspring. Breeding occurs from December to April. Nests are constructed out of sticks high atop cypress, mangrove, or other trees in marshy woodlands. Wood storks nest colonially with from 5 to 25 nests in a single tree.

Females lay 2 to 4 (usually 3) eggs per clutch. Incubation lasts 28 to 32 days and the young fledge after 55 to 60 days. Woodstorks do not begin to breed until they are 4 years old. (Ehrlich, et al., 1988; The Georgia Museum of Natural History and Georgia Department of Natural Resources, 2000; Wolkomir and Wolkomir, 2001)

  • Breeding season
    December to April
  • Range eggs per season
    2 to 4
  • Average eggs per season
    3
    AnAge
  • Range time to hatching
    28 to 32 days
  • Range fledging age
    55 to 60 days
  • Average age at sexual or reproductive maturity (female)
    4 years
  • Average age at sexual or reproductive maturity (male)
    4 years

Both the male and female take part in nest building, incubation and the feeding of their semi-altricial young. Chicks are fed regurgitated fish and are dependent on their parents for 55 to 60 days after they hatch. (Ehrlich, et al., 1988; The Georgia Museum of Natural History and Georgia Department of Natural Resources, 2000)

  • Parental Investment
  • altricial
  • pre-fertilization
    • provisioning
    • protecting
      • female
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • male
      • female
  • pre-weaning/fledging
    • provisioning
      • male
      • female
    • protecting
      • male
      • female

Lifespan/Longevity

We do not have information on lifespan/longevity for this species at this time.

Behavior

Like their close relatives, vultures of the family Cathartidae (Mindell et al., 1998), storks are soaring birds that will ride thermals to altitudes of up to 300 meters or more to get to feeding grounds up to 130 kilometers away (Klinkenberg, 1998). They are known to be incredible acrobats when descending, performing marvelous turns, dives, and rolls. They are highly gregarious birds occurring in small to very large flocks and they build their nests in large colonies with other storks.

The formation of flocks is thought to be triggered when the birds smell exposed mud at low tides. These areas are often favorable feeding grounds. Like other migrating birds, wood storks may locate their nesting grounds by recognizing geographical landmarks and sensing magnetic fields (Wolkomir and Wolkomir, 2001). (Klinkenberg, 1998; Mindell, et al., 1998; Wolkomir and Wolkomir, 2001)

Home Range

We do not have information on home range for this species at this time.

Communication and Perception

Like other migrating birds, wood storks may locate their nesting grounds by recognizing geographical landmarks and sensing magnetic fields. (Wolkomir and Wolkomir, 2001)

Food Habits

Adult wood storks eat small fish, frogs, mollusks, snails, insects, and aquatic invertebrates. It has been calculated that a 2.5 kilogram bird would eat more than half a kilogram of fish daily. Wood storks wade through shallow water feeling for movement and snap their bill shut when they touch a fish. Vision is not as important as touch, and the bill-snapping reflex of the stork is one of the fastest reflexes known in vertebrates, taking only about 25 thousandths of a second (Wolkomir and Wolkomir, 2001). It was also recently discovered that wood storks often leave the roost at night to catch prey or fish during nocturnal low tides. This allows them to feed without the competition of other large shorebirds such as great egrets. (Bryan, et al., 2001b; Wolkomir and Wolkomir, 2001)

  • Animal Foods
  • amphibians
  • fish
  • insects
  • mollusks

Predation

The greatest threat to wood storks are raccoons (Procyon lotor) that climb to the nests to eat the chicks. Alligators (Alligator mississippiensis) may also pose a problem to unwary birds. (Klinkenberg, 1998)

Ecosystem Roles

Wood storks and other wading birds are an integral part of the marshland food chain along with other reptilian and mammalian predators. (Klinkenberg, 1998)

Economic Importance for Humans: Positive

We do not have information on economic importance for this species at this time.

Economic Importance for Humans: Negative

There are no known adverse affects of wood storks on humans.

Conservation Status

In the 1930's an estimated 20,000 wood stork pairs were nesting in the United States. In 1978 only 2,500 pairs were recorded and wood storks were placed on the Endangered Species List in 1984. A recent survey of nesting pairs counted 5,500 pairs (Klinkenberg, 1998). If the species grows to 6,000 nesting pairs it may be reclassified to "threatened" instead of "endangered". The best way to help the species is to preserve wetlands, limit water management, and reduce heavy metal pollution such as mercury which can be lethal to the storks (Bryan et al., 2001a).

Historically the largest American population of wood storks has been in Florida's Big Cypress National Preserve and the Everglades, but because of a decline in wetland habitat and water management, colonies seem to be migrating northward (Brooks, 2001).

Wood storks are listed as endangered on the US Federal List and are protected under the US MBTA. (Brooks, 2001; Bryan, et al., 2001a; Klinkenberg, 1998)

Other Comments

Wood storks are the only nesting storks in the United States and our largest wading bird. They are also endearingly called "flinthead" or "ironhead" by some.

Traditionally in Austrian and German folklore, storks were said to deliver babies. These stories have now been passed on to the Americas. Wood storks are exceptionally serene animals that can live harmoniously alongside humans if left undisturbed. (Wolkomir and Wolkomir, 2001)

Contributors

Alaine Camfield (editor), Animal Diversity Web.

Sean Carroll (author), Western Maryland College, Randall L. Morrison (editor), Western Maryland College.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

Neotropical

living in the southern part of the New World. In other words, Central and South America.

World Map

acoustic

uses sound to communicate

altricial

young are born in a relatively underdeveloped state; they are unable to feed or care for themselves or locomote independently for a period of time after birth/hatching. In birds, naked and helpless after hatching.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

brackish water

areas with salty water, usually in coastal marshes and estuaries.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

colonial

used loosely to describe any group of organisms living together or in close proximity to each other - for example nesting shorebirds that live in large colonies. More specifically refers to a group of organisms in which members act as specialized subunits (a continuous, modular society) - as in clonal organisms.

endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

estuarine

an area where a freshwater river meets the ocean and tidal influences result in fluctuations in salinity.

fertilization

union of egg and spermatozoan

internal fertilization

fertilization takes place within the female's body

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

magnetic

(as perception channel keyword). This animal has a special ability to detect the Earth's magnetic fields.

marsh

marshes are wetland areas often dominated by grasses and reeds.

migratory

makes seasonal movements between breeding and wintering grounds

monogamous

Having one mate at a time.

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

piscivore

an animal that mainly eats fish

seasonal breeding

breeding is confined to a particular season

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

social

associates with others of its species; forms social groups.

swamp

a wetland area that may be permanently or intermittently covered in water, often dominated by woody vegetation.

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

terrestrial

Living on the ground.

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

visual

uses sight to communicate

References

Brooks, B. 2001. Wood Stork (Mycteria americana). Endangered Species Update, 18: S38.

Bryan, A., J. Snodgrass, J. Robinette, J. Daly, L. Brisbin. 2001b. Nocturnal activities of post-breeding Wood Storks. The Auk, 118 (2): 508-313.

Bryan, A., C. Jagoe, H. Brant, J. Gariboldi, G. Masson. 2001a. Mercury concentrations in post-fledging Wood Storks. Waterbirds, 24(2): 277-281.

Ehrlich, P., D. Dobkin, D. Wheye. 1988. The Birder's Handbook: A field guide to the natural history of North American birds. New York: Simon & Schuster Inc.

Farrand, J. 1983. Audubon Society Master Guide to Birding. Alfred A. Knopf.

Klinkenberg, J. 1998. Coming back on its own terms (Wood Storks adapt to changes and thrive). National Wildlife, April-May: 52.

Mindell, D., M. Sorenson, D. Dimcheff. 1998. Multiple independent origins of mitochondrial gene order in birds. Proceedings of the National Academy of Sciences, 95 (18): 10693-10697.

Ramo, C., B. Busto. 1992. Nesting failure of the Wood Stork in a neotropical wetland. The Condor, 94 (3): 777-781.

The Georgia Museum of Natural History, , Georgia Department of Natural Resources. 2000. "Storks" (On-line). Accessed January 21, 2004 at http://museum.nhm.uga.edu/gawildlife/birds/Ciconiiformes/mamericana.html.

Wolkomir, R., J. Wolkomir. 2001. In search of sanctuary: As its Florida habitat disappears, the American Wood Stork, our largest wading bird, is migrating northward to new nesting grounds. Smithsonian, February: 72.

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