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Sep 25 2011

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Wood Stork (Mycteria americana)

Wood Stork

[order] CICONIIFORMES | [family] Ciconiidae | [latin] Mycteria americana | [authority] Linnaeus, 1758 | [UK] Wood Stork | [FR] Tantale d’Amerique | [DE] Waldstorch | [ES] Tantalo Americano | [NL] Kaalkopooievaar

Subspecies

Genus Species subspecies Region Range
Mycteria americana NA, LA se USA to n Argentina

Genus

Mycteria is a genus of large tropical storks with representatives in the Americas, east Africa and southern and southeastern Asia. Two species have “ibis” in their scientific or old common names, but they are not related to these birds and simply look more similar to an ibis than do other storks. The Mycteria storks are large birds, typically around 90?100 cm in length with a 150 cm wingspan. The body plumage is mainly white in all the species, with black in the flight feathers of the wings. The Old World species have a bright yellow bill, red or yellow bare facial skin and red legs, but these parts are much duller in the Wood Stork of tropical America. Juvenile birds are a duller version of the adult, generally browner, and with a paler bill. They are broad-winged soaring birds that fly with the neck outstretched and legs extended. They are resident breeders in lowland wetlands with trees in which build large stick nests.
Two prehistoric relatives of the Wood Stork have been described from fossils. 1) Mycteria milleri (Miller’s Stork) (Valentine Middle Miocene of Cherry County, USA) – formerly Dissourodes. 2) Mycteria wetmorei (Wetmore’s Stork) (Late Pleistocene of W and SE USA, and Cuba)
The latter seems to have been a larger sister species of the Wood Stork, which it replaced in prehistoric North America. Late Miocene tarsometatarsus fragments (Ituzaingo Formation at Parana, Argentina) are somewhat similar to Mycteria but still distinct enough to be probably a distinct genus, especially considering their age. A Late Pleistocene distal radius from San Josecito Cavern (Mexico) may belong in this genus or in Ciconia. A “ciconiiform” fossil fragment from the Touro Passo Formation found at Arroio Touro Passo (Rio Grande do Sul, Brazil) might be of the living species M. americana; it is at most of Late Pleistocene age, a few 10.000s of years.

Physical charateristics

This is a large bird, 85-115 cm tall, with a wingspan of 150-165 cm. Adults are completely white except for wing tips and tail, which are black with a greenish and purplish sheen. Perhaps the most distinctive feature is the head, which is unfeathered, scaly and grey in adults (hence the local name ?Flinthead?). The bill is large, black to blackish grey, massive, thick at the base and tapering in a gentle decurve. Legs and feet are dark, with flesh colored or pink (breeding season) toes. The young and subadults are similar to adults, but have greyish feathers on the head and neck, and a pale yellow bill that darkens with age. In flight, Wood Storks fly with their legs straight out behind, often alternately flapping and gliding, or soaring with wings held straight out.

Listen to the sound of Wood Stork

[audio:http://www.planetofbirds.com/MASTER/CICONIIFORMES/Ciconiidae/sounds/Wood Stork.mp3]

Copyright remark: Most sounds derived from xeno-canto

recorded by Bernabe Lopez-Lanus


wingspan min.: 150 cm wingspan max.: 165 cm
size min.: 85 cm size max.: 115 cm
incubation min.: 27 days incubation max.: 32 days
fledging min.: 50 days fledging max.: 32 days
broods: 1   eggs min.: 1  
      eggs max.: 5  

Range

North America, Latin America : Southeast USA to North Argentina

Habitat

Because it captures fish by groping with its open bill in water, the stork depends on low water levels to concentrate fish in adequate numbers to feed its young. This specialization results in irregular nesting cycles initiated by adequate water levels. During years of drought, some birds do not breed, while others move to areas with adequate water levels to initiate nesting. Wood Storks can be found feeding in shallow water in both freshwater and coastal wetlands, including tidal creeks and flats, marshes, cypress swamps, ponds, ditches, and flooded fields. The Wood Stork eats fish, small reptiles, amphibians, and mammals, as well as other aquatic organisms.

Reproduction

This species nests in colonies of up to tens of thousands of pairs, but more usually tens to hundreds. Colonies are in areas surrounded by water, often in cypress swamps, mangrove swamps, coastal islands, islands within ponds and impoundments. Courtship precedes nestbuilding, with males displaying, vocalizing and defending a nest site, and females approaching to display to males. Males and females probably do not stay paired for more than a single nesting season.
Generally nests are built of sticks, and are placed in larger trees at or above the canopy level. The nest is a very shallow cup, often described as a sort of platform. Both members of the pair build the nest, incubate eggs, and rear young. Between 1 and 5 creamy white eggs (more usually 2-4) are laid over the course of 4-9 days, and incubated for 27-32 days. Young hatch sequentially, are covered with white down at hatching, and must be brooded constantly for the first week. After that time, they can stand at 2-3 weeks, and walk or climb away from the nest at 3-4 weeks. Young feed voraciously and call loudly during the first five weeks of age.
Parents feed young by regurgitating food directly into their bills; when its hot, the parents may regurgitate water over the chicks to cool them. Storks also defecate on their legs as a way to use evaporative cooling-thus their dark-colored legs often appear white. Young begin to leave the nest for short trips between 50 and 60 days of age, though parents may continue to feed them for some time thereafter. No parental care is shown after the young leave the nest.

During the breeding period, each nest may need 150 kg of fish to produce between 1 and 3 nestlings. As a result, colonies tend to produce a lot of feces, which places a lot of nutrients into the soil and surrounding water. This may result in local changes in the appearance and types of vegetation in the colony, as well as increased production and densities of aquatic animals in the immediate vicinity of the colony.

Feeding habits

The Wood Stork has an almost unique foraging technique. It generally walks with its bill in the water partially open, swinging the bill in an arc or probing with it in mud and vegetation. When the bill is stimulated by contact with prey, they are captured with an extremely rapid reflex snap, measured at about 25 milliseconds (one of the fastest reflex actions measured in the animal world). Storks may also use their feet to stir the water, presumably flushing fishes and invertebrates towards their open bills. They often flick their wings open and shut, possibly also to scare prey towards the bill.
Storks feed mostly on fishes, but will also take a variety of other aquatic organisms, including insects, crayfishes, shrimps an crabs, amphibians, snakes, small alligators, and occasionally small birds and mammals. Generally, storks tend to avoid the smallest prey and take prey averaging 40 – 85 mm in length.

Video Wood Stork

httpv://www.youtube.com/watch?v=fa33hxEYxfQ

copyright: youtube


Conservation

This species has an extremely large range, and hence does not approach the thresholds for Vulnerable under the range size criterion (Extent of Occurrence <20,000 km2 combined with a declining or fluctuating range size, habitat extent/quality, or population size and a small number of locations or severe fragmentation). Despite the fact that the population trend appears to be decreasing, the decline is not believed to be sufficiently rapid to approach the thresholds for Vulnerable under the population trend criterion (>30% decline over ten years or three generations). The population size may be moderately small to large, but it is not believed to approach the thresholds for Vulnerable under the population size criterion (<10,000 mature individuals with a continuing decline estimated to be >10% in ten years or three generations, or with a specified population structure). For these reasons the species is evaluated as Least Concern.
This species breeds in the United States from southern North Carolina through the coastal plain of South Carolina, Georgia, and occasionally in Alabama, and throughout peninsular Florida. Outside of the United States, Wood Storks are found breeding from Mexico south to Argentina where suitable habitat is available: east of the Andes from Colombia to Argentina and eastern Bolivia; west of the Andes from Colombia through Ecuador. In Suriname very common in the coastal regions with open water surface.
Wood Stork status Least Concern

Migration

Post-breeding dispersal in USA and Mexico. In tropical South America out of breeding season wanders about, looking for optimum conditions, e.g. regular movements between Orinoco and Amazon basins, but also up and down Amazon and even regularly across Andes of South Colombia at 2000 m. Some North-South movement, with many birds passing southern summer in Brazil, where absent in winter. Flocks of 500-1000 recorded on migration, though large ones may well occur. Can commute over large distances during breeding.

Distribution map

Wood Stork distribution range map

Literature

Title ORGANOCHLORINE RESIDUES AND EGGSHELL THINNING IN WOOD STORKS AND ANHINGAS
Author(s): HARRY M. OHLENDORF, ERWIN E. KLAAS and T. EARL KAISER
Abstract: All 10 Wood Stork eggs collected at Merritt Island..[more]..
Source: Wilson Bulletin: Vol. 90, No. 4, October-December, 1978

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