Wood stork

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Wood stork
WoodStorkWhole.JPG
Pond, Tampa Bay, Florida
About this sound Chick vocalizations 
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Aves
Order: Ciconiiformes
Family: Ciconiidae
Genus: Mycteria
Species: americana
Binomial name
Mycteria americana
Linnaeus, 1758

The wood stork (Mycteria americana) is a large American wading bird in the stork family Ciconiidae. It was formerly called the "wood ibis", though it is not an ibis. As of June 26, 2014 it is classified as a threatened species in the United States by the U.S. Fish & Wildlife Service.[2][3]

Taxonomy and etymology[edit]

Wood stork alighting, Hontoon Dead River, in Florida

This species seems to have evolved in tropical regions; its North American presence probably postdates the last ice age. A fossil fragment from the Touro Passo Formation found at Arroio Touro Passo (Rio Grande do Sul, Brazil) might be of the living species; it is at most from the Late Pleistocene age, a few 10,000s of years ago.[4] North American fossils from that time are of an extinct larger relative, M. wetmorei. This was probably a sister species; both occurred sympatrically on Cuba at the end of the Pleistocene.[5]

Of the extant members of the genus Mycteria, this bird is basal. The clade that it is basal to is the clade that has the yellow-billed stork being basal to the milky stork and the painted stork.[6]

Description[edit]

The wood stork's head much resembles that of an ibis
Wood stork in flight at Harris Neck National Wildlife Refuge

The adult is a large bird which stands 83 to 115 cm (33–45 in) tall and spans 140 to 180 cm (55–71 in) across the wings. Males typically weigh 2.5 to 3.3 kg (5.5–7.3 lb), with a mean weight of 2.7 kg (6.0 lb); females weigh 2.0 to 2.8 kg (4.4–6.2 lb), with a mean weight of 2.42 kg (5.3 lb).[7][8] Another mean estimated weight for the species was 2.64 kg (5.8 lb).[9] However, exceptionally large males are sometimes found and these can weigh up to 4.5 kg (9.9 lb).[10] It appears all white on the ground, with blackish-gray legs and pink feet. In flight, the trailing edge of the wings is black. The head is dark brown with a bald, black face, and the thick down-curved bill is dusky yellow. The bare head and the long bill, which can measure up to 25.5 cm (10.0 in) in length, render the wood stork distinctive from other large waders in its range.[11] The standard scientific measurements of the wood stork are as follows: the wing is 42–49 cm (17–19 in), the culmen is 19–25 cm (7.5–9.8 in) and the tarsus is 17.5–21.5 cm (6.9–8.5 in).[12]

When the chicks hatch, they have a sparse coat of grey down, protoptiles, which is replaced by a dense, wooly, and white down, mesoptiles, in about 10 days. Chicks grow fast, being about half of the height of the adult by three to four weeks after hatching. By the sixth and seventh weeks, the plumage on the head and neck turns smokey grey. When fledged, they resemble the adult, differing only in that they have a feathered head and a yellow bill.[13] Juvenile birds are a duller version of the adult, generally browner on the neck, and with a paler bill.[11]

Distribution and habitat[edit]

This is a subtropical and tropical species which breeds in much of South America, Central America and the Caribbean. The wood stork is the only stork that presently breeds in North America. In the United States there is a small breeding population in Florida, Georgia, and South Carolina, along with a recently discovered rookery in southeastern North Carolina.[3]

This stork is suggested to be able to adapt to a variety of habitats[14] that are in the tropics and have fluctuating water levels.[15] The main habitats are those where it nests over water and those where it is surrounded by water. In freshwater habitats, it generally prefers forests that are dominated by trees of the genus Taxodium, while in estuaries, it prefers mangrove forests.[14]

Behaviour[edit]

Breeding[edit]

Nesting colony in Georgia, US

A resident breeder in lowland wetlands with trees, the wood stork builds a large stick nest in a forest tree.[16] In freshwater habitats, it prefers to nest in trees that are larger in diameter.[14] It nests colonially, with up to 25 nests in one tree.[16] The height of these nests is variable, with some nests located in shorter mangrove trees being at heights of about 2.5 metres (8.2 ft), compared to a height of about 6.5 metres (21 ft) for taller mangrove trees.[17] For Taxodium trees, it generally nests near the top branches, frequently between 18 and 24 metres (59 and 79 ft) above the ground.[15]

The nest itself is built by the male[18] from sticks[19] and greenery[20] collected from the colony and the surrounding area.[18] The greenery usually starts to be added before the eggs are laid but after the main structure of twigs is completed. It is continued to be added during incubation, with the addition of greenery decreasing after the eggs are hatched. The greenery functions to insulate the nest.[20] When complete, the nest is about one metre (3.3 ft) in diameter.[18]

Breeding is initiated by a drop in the water level combined with an increased density of fish. This is because a decrease in the water level and an increased density of fish allows for an adequate amount of food for the nestlings.[15] This can occur anywhere between November and August. After it starts, breeding takes about four months to complete.[21]

This bird lays one clutch of three to five cream coloured eggs that are about 68 by 46 millimetres (2.7 by 1.8 in) in size.[19] These eggs are usually laid one to two days apart[18] and incubated for 27 to 32 days,[19] starting with when the first egg is laid,[15] by both sexes. During the first week of incubation, the parents do not go far from the colony, with the exception of the short trips to forage, drink, and collect nesting material carried out by the non-incubating bird. After the first week, the non-incubating bird spends less time in the colony, although the eggs are never left unattended. After a few hours of incubation, this bird sometimes takes a break to stretch, preen itself, rearrange nest material, or turn the eggs.[18] The eggs hatch in the order in which they were laid, with an interval of a few days between when each egg hatches.[15]

The chicks hatch altricial, unable to move, and weigh an average of 62 grams (2.2 oz).[13] They are brooded for the first week after hatching, and after that when it is raining and at night.[18] The chicks are not left alone until at least three weeks of age, with one parent foraging while the other guards the nest and chicks. When the chicks are at least three weeks old, they are large enough to stay and protect the nest. This coincides with the chicks getting more aggressive when presented with foreign objects or organisms. They fledge 60 to 65 days after hatching,[13] and reach sexual maturity four years of age, although they usually do not successfully fledge chicks until their fifth year of age.[21]

Feeding[edit]

During the dry season, the wood stork eats mostly fish and is supplemented by insects. During the wet season, on the other hand, fish make up about half the diet, crabs make up about 30%, and insects and frogs make up the rest.[22] The wood stork eats larger fish more often than smaller fish, even in some cases where the latter is more abundant.[23] It is estimated that an adult wood stork needs about 520 grams (1.15 lb) per day to sustain itself. For a whole family, it is estimated that about 200 kilograms (440 lb) is needed per breeding season.[15]

The wood stork usually forages in flocks when not breeding, and alone and in small groups when it is breeding. In the dry season, this bird generally forages by slowly walking forward with its bill submerged in the water while groping for food. During the wet season, this method is used about 40% of the time to catch food. During this time, foot stirring, where the stork walks very slowly with the bill in water while pumping its foot up and down before every step, it used about 35% of the time. Both of these methods are non-visual.[22]

Because of its non-visual foraging methods, the wood stork requires shallow water and a high density of fish to forage successfully. The water that it forages in during the dry season average about 17 centimetres (6.7 in) in depth, while during the wet season, the water usually is about 10 centimetres (3.9 in). In the dry season, this stork prefers to forage in waters with no emergent vegetation, whereas in the wet season, it prefers areas with vegetation emerging between 10 and 20 centimetres (3.9 and 7.9 in) above the surface on average.[22] This bird can travel over 80 kilometres (50 mi) to reach foraging sites, lending it access to a wide variety of habitats.[24]

Both sexes feed the chicks by regurgitating meals onto the nest floor. The chicks are mainly fed fish that are between 2 and 25 centimetres (0.79 and 9.84 in) in length, with the length of the fish usually increasing as the chicks get older. The amount of food that the chicks get changes over time, with more being fed daily from hatching to about 22 days, when food intake levels off. This continues until about 45 days, when food consumption starts to decrease. Overall, a chick eats about 16.5 kilograms (36 lb) before it fledges.[13]

Aggressiveness[edit]

Wood storks without a nest occasionally try to take over others' nests. Such nest take-overs are performed by more than one bird. The young and eggs are thrown out of the nest within about 15 minutes. If only one stork is attending the nest when it is forced out, then it will usually wait for its mate to try to take the nest back over.[25] Chicks do not display aggression until about three weeks after they hatch.[13]

Flight[edit]

When flying, this bird utilizes two different techniques. When it is not sufficiently warm and clear, such as in the late afternoon and on cloudy days, this stork alternates between flapping its wings and gliding for short periods of time. When it is warm and clear, this bird glides after it reaches an altitude of at least 610 metres (2,000 ft) through continuously flapping its wings. It can glide in this manner for distances ranging from 16 to 24 kilometres (9.9 to 14.9 mi). It does not have to flap its wings during this time because the warm, rising air currents are strong enough to support its weight.[15] Because of the energy that is conserved by gliding, this stork usually uses this method to fly to more distant areas.[26]

When flying to foraging areas, the wood stork has an average speed of about 24.5 kilometres per hour (15.2 mph). When it flies by flapping its wings, it goes about 34.5 kilometres per hour (21.4 mph), whereas when it glides, it flies at speeds of about 20 kilometres per hour (12 mph).[26]

Predators and parasites[edit]

Each adult will defend its nest against various predators. Corvids, vultures, grackles and striped skunks will attempt to pick off eggs.[27] Raccoons are the leading predator of nests, and can cause almost complete colony nesting failure when water dries under nests in drought years since they can easily access the nest using dry ground under the tree.[28]

Status[edit]

Globally, the wood stork is considered least concern by the IUCN due to its large range.[1] In the United States, this bird is considered to be threatened, a recovery from its endangered status, which it held from 1984 to 2014 because of a decline in its population.[3] Similarly, in the state of Santa Catarina, Brazil, its decline seems to have been reversed: after an absence between the late 1960s and the mid-1990s, the species is now again regularly encountered there, in particular in the Tubarão River region.[29] It is likely that the Paraná River region's wetlands served as a stronghold of the species, from where it is now re-colonizing some of its former haunts.[30]

Threats[edit]

Disturbance by tourists can have a large effect on nesting success, with a study with nests that boats passed by within about 20 metres (66 ft) of fledging an average of .1 chicks, compared to the normal rate for that area of about .9 chicks fledged per nest. Pedestrians watching at a distance of at least 75 metres (246 ft) did not significantly affect nesting success.[31]

References[edit]

  1. ^ a b BirdLife International (2012). "Mycteria americana". IUCN Red List of Threatened Species. Version 2013.2. International Union for Conservation of Nature. Retrieved 26 November 2013. 
  2. ^ "Wood stork (Mycteria americana) Species Profile". U.S. Fish & Wildlife Service Environmental Conservation Online System. U.S. Fish & Wildlife Service. 31 August 2014. 
  3. ^ a b c "Wood stork off endangered list after recovery in U.S. Southeast". Reuters. 26 June 2014. Retrieved 1 July 2014. 
  4. ^ Schmaltz Hsou, Annie (20 June 2007). O estado atual do registro fóssil de répteis e aves no Pleistoceno do Estado do Rio Grande do Sul, Brasil [The current state of the fossil record of Pleistocene reptiles and birds of Rio Grande do Sul] (PDF) (Speech) (in Portuguese). Quaternário do RS: integrando conhecimento, Canoas, Rio Grande do Sul, Brazil. 
  5. ^ Suarez, William; Olson, Storrs L. (2003). "New Records of Storks (Ciconiidae) from Quaternary Asphalt Deposits in Cuba" (PDF). Condor. 105 (1): 150–154. doi:10.1650/0010-5422(2003)105[150:NROSCF]2.0.CO;2. 
  6. ^ Sheldon, Frederick H.; Slikas, Beth (1997). "Advances in Ciconiiform systematics 1976-1996". Colonial Waterbirds. 20 (1): 106. ISSN 0738-6028. doi:10.2307/1521772. 
  7. ^ "Potential risk to wood storks (Mycteria americana) from mercury in Carolina Bay fish". Environmental Pollution. 120: 405–413. 2002-02-05. doi:10.1016/s0269-7491(02)00112-4. 
  8. ^ CRC Handbook of Avian Body Masses, 2nd Edition by John B. Dunning Jr. (Editor). CRC Press (2008). ISBN 978-1-4200-6444-5.
  9. ^ Palmer, R. S. (1962). Handbook of North American birds, Volume 1, Loons through Flamingos. Yale Univ. Press, New Haven, CT.
  10. ^ "Wood Stork (Mycteria americana)". Pelotes Island Nature Preserve. 1997-01-02. Retrieved 2013-01-30. 
  11. ^ a b "Everglades National Park (Page 2)". ParkVision: Images of America's National Parks. Retrieved 2013-01-30. 
  12. ^ Hancock, James A.; Kushlan, James A.; Kahl, M. Philip (1992). Storks, Ibises, and Spoonbills of the World. Academic Press. ISBN 978-0-12-322730-0. 
  13. ^ a b c d e Kahl, M. Philip (1962). "Bioenergetics of growth in nestling wood storks". The Condor. 64 (3): 169–183. ISSN 0010-5422. doi:10.2307/1365200. 
  14. ^ a b c Rodgers, James A.; Schwikert, Stephen T.; Shapiro-Wenner, Anne (1996). "Nesting habitat of wood storks in north and central Florida, USA". Colonial Waterbirds. 19 (1): 1. ISSN 0738-6028. doi:10.2307/1521802. 
  15. ^ a b c d e f g Kahl, M. Philip (1964). "Food ecology of the wood stork (Mycteria americana) in Florida". Ecological Monographs. 34 (2): 97–117. ISSN 0012-9615. doi:10.2307/1948449. 
  16. ^ a b Ehrlich, Paul R.; Dobkin, David S.; Wheye, Darryl (1992). Birds in Jeopardy. Stanford, CA: Stanford University Press. p. 18. ISBN 0-8047-1967-5. 
  17. ^ Llanes-Quevedo, Alexander; Rodríguez-Ochoa, Alejandro; Rodríguez, Carlos Frankel (2015). "Reproducción y hábitat de cría de Mycteria americana (Aves: Ciconiidae) en Cuba" [Reproduction and nesting habitat of Mycteria americana (Aves: Ciconiidae) in Cuba]. 4 (1): 96–101. 
  18. ^ a b c d e f Clark, E. Scott (1980). "The attentiveness and time budget of a pair of nesting wood storks". Proceedings of the Colonial Waterbird Group. 3: 204–215. ISSN 1556-5785. doi:10.2307/4626715. 
  19. ^ a b c Hauber, Mark E. (1 August 2014). The Book of Eggs: A Life-Size Guide to the Eggs of Six Hundred of the World's Bird Species. Chicago: University of Chicago Press. p. 106. ISBN 978-0-226-05781-1. 
  20. ^ a b Rodgers, James A.; Wenner, Anne S.; Schwikert, Stephen T. (1988). "The use and function of green nest material by wood storks". The Wilson Bulletin. 100 (3): 411–423. ISSN 0043-5643. doi:10.2307/4162606. 
  21. ^ a b Elliott, Andrew; Garcia, E.F.J.; Kirwan, G.M.; Boesman, P. (2017). del Hoyo, Josep; Elliott, Andrew; Sargatal, Jordi; Christie, David A.; de Juana, Eduardo, eds. "Wood Stork (Mycteria americana)". Handbook of the Birds of the World Alive. Barcelona, Spain: Lynx Edicions. Retrieved 26 August 2017. (Subscription required (help)). 
  22. ^ a b c González, José A. (1997). "Seasonal Variation in the Foraging Ecology of the Wood Stork in the Southern Llanos of Venezuela". The Condor. 99 (3): 671–680. ISSN 0010-5422. doi:10.2307/1370479. 
  23. ^ Ogden, John C.; Kushlan, James A.; Tilmant, James T. (1976). "Prey selectivity by the wood stork". The Condor. 78 (3): 324. ISSN 0010-5422. doi:10.2307/1367691. 
  24. ^ Kushlan, James A. (1986). "Responses of wading birds to seasonally fluctuating water levels: Strategies and their limits". Colonial Waterbirds. 9 (2): 155. ISSN 0738-6028. doi:10.2307/1521208. 
  25. ^ Bryan, A. Lawrence; Coulter, Malcolm C. (1991). "Conspecific aggression in a wood stork colony in Georgia". The Wilson Bulletin. 103 (4): 693–697. ISSN 0043-5643. 
  26. ^ a b Bryan, A. Lawrence; Coulter, Malcolm C. (1987). "Foraging flight characteristics of wood storks in east-central Georgia, U.S.A.". Colonial Waterbirds. 10 (2): 157. ISSN 0738-6028. doi:10.2307/1521254. 
  27. ^ "Bio Facts: Wood Stork". Jacksonville Zoo and Gardens. Archived from the original on 12 May 2008.  External link in |website= (help)
  28. ^ "Wood Stork — Behavior — Birds of North America Online". Bna.birds.cornell.edu. Retrieved 2013-01-30. 
  29. ^ Amorim, James Faraco; Piacentini, Vítor de Queiroz (2006). "Novos registros de aves raras em Santa Catarina, Sul do Brasil, incluindo os primeiros registros documentados de algumas espécies para o Estado" [New records of rare birds, and first reports of some species, in the state of Santa Catarina, southern Brazil] (PDF). Revista Brasileira de Ornitologia (in Portuguese and English). 14 (2): 145–149.  Electronic supplement
  30. ^ Bencke, Glayson Ariel (22 June 2007). Avifauna atual do Rio Grande do Sul, Brasil: aspectos biogeográficos e distribucionais [The Recent avifauna of Rio Grande do Sul: Biogeographical and distributional aspects] (PDF) (Speech) (in Portuguese). Quaternário do RS: integrando conhecimento, Canoas, Rio Grande do Sul, Brazil. 
  31. ^ Bouton, Shannon N.; Frederick, Peter C.; Rocha, Cristiano Dosualdo; Barbosa Dos Santos, Alexandre T.; Bouton, Tara C. (2005). "Effects of tourist disturbance on wood stork nesting success and breeding behavior in the Brazilian Pantanal". Waterbirds. 28 (4): 487–497. ISSN 1524-4695. doi:10.1675/1524-4695(2005)28[487:EOTDOW]2.0.CO;2. 

Further reading[edit]

  • Alsop, Fred J. III (2002). Birds of Texas. New York City: DK Publishing, Inc. ISBN 0-7894-8388-2. 

External links[edit]