Milky stork

{{Short description|Species of bird}} {{speciesbox | image = Mycteria cinerea, Singapore 3.jpg | image_caption = An individual foraging among bulrush in Singapore | status = EN | status_system = IUCN3.1 | status_ref = <ref name=IUCN>{{cite iucn |title=''Mycteria cinerea'' |author=BirdLife International |year=2023 |article-number=e.T22697651A183200130 |doi=10.2305/IUCN.UK.2023-1.RLTS.T22697651A183200130.en}}</ref> | status2 = CITES_A1 | status2_system = CITES | status2_ref = <ref name=IUCN/> | genus = Mycteria | species = cinerea | authority = (Raffles, 1822) | range_map = Milkystorkrange.png | range_map_caption = {{legend0|#22b14e|&nbsp;resident extant range}} }}

The '''milky stork''' ('''''Mycteria cinerea''''') is a stork species inhabiting predominantly mangroves in Southeast Asia. It is native to Cambodia, Vietnam, Malaysia and Indonesia. It is currently included in the genus ''Mycteria'', is around {{cvt|91-97|cm}} tall, with a wingspan of {{cvt|43.5-50|cm}} and a tail around {{cvt|14.5-17|cm}}. Its plumage is white apart from a few feathers at the wings and tail. Since the 1980's, the global milky stork population has declined from 5,000 to 2,000 individuals due to habitat destruction, overfishing and illegal smuggling of chicks. It is listed as Endangered on the IUCN Red List.

==Taxonomy and systematics== The milky stork was formerly placed in the genus ''Ibis'', with the binomial name ''Ibis cinereus'', but is now included in the ''Mycteria'' due to large similarities in appearance and behaviour to the three other storks in this genus (the wood stork, yellow-billed stork, and painted stork).<ref name = "Kahl1972">{{cite journal|author=Kahl M. P. |title=Comparative ethology of the Ciconiidae. The wood-storks (Genera ''Mycteria'' and ''Ibis'')|journal=Ibis|volume=114|pages=15–29|doi=10.1111/j.1474-919X.1972.tb02586.x|year=2008}}</ref> Phylogenetic studies based on DNA hybridization and cytochrome oxidase b have demonstrated that the milky stork shares a clade with other ''Mycteria'', and forms a sister pair of species with the painted stork.<ref>{{cite journal|author=Slikas B.|title=Phylogeny of the avian family Ciconiidae (storks) based on cytochrome b sequences and DNA-DNA hybridization distances|journal=Molecular Phylogenetics and Evolution|volume=8|issue=3|pages=275–300|pmid=9417889|year=1997|doi=10.1006/mpev.1997.0431|doi-access=free|bibcode=1997MolPE...8..275S }}</ref>

==Description== ===Adult=== This medium stork stands 91–97&nbsp;cm tall, making it slightly smaller than the closely related painted stork.<ref name=IUCN/><ref name = "Hancock">Hancock JA, Kushlan JA, Kahl, MP. (1992). ''Storks, Ibises and Spoonbills of the World''. Academic Press.</ref> The adult plumage is completely white except for black flight feathers of the wing and tail, which also have a greenish gloss.<ref name = "Hancock"/> Wing length measures 435–500&nbsp;mm<ref name = "Delacour">Delacour J, Jabouille P. (1931).''Les oiseaux de I'Indochine Francaise'', 1–4. Paris: Exposition Coloniale Internationale.</ref><ref name = "Kuroda">Kuroda N. (1936). ''Birds of the Island of Java''. Tokyo.</ref> and the tail measures 145–170&nbsp;mm.<ref name = "Hancock"/><ref name = "Kuroda"/> The extensive white portion of the plumage is completely suffused with a pale creamy yellow during the breeding season, hence the term "milky".<ref name="Kahl1972"/><ref name = "Hancock"/> This creamy tint is absent from the plumage during breeding.<ref name = "Elliot">Elliot A. (1992). "Family Ciconiidae (storks)", pp. 436–465 in del Hoyo J, Elliot A, Sargatal J. (eds.) ''Handbook of the birds of the world''. Vol. I. Lynx Edicions, Barcelona.</ref> The wing coverts and back feathers are paler and have an almost white terminal band.<ref name="Kahl1972"/><ref name = "Hancock"/>

The bare facial skin is greyish or dark maroon; with black, irregular blotches.<ref name = "Hancock"/> During breeding, the bare facial skin is deep wine red with black markings on the lores by the bill base and gular region, with a ring of brighter red skin around the eye.<ref name = "Kahl1972"/><ref name ="Hancock"/><ref name = "Elliot"/> Soon after courtship, the facial skin fades to paler orange-red.<ref name = "Hancock"/> Breeding birds also show a narrow pinkish band of bare skin along the underside of the wing.<ref name = "Hancock"/>

The downcurved bill is dull pinkish yellow and sometimes tipped white. The culmen length measures 194 – 275mm.<ref name = "Delacour"/><ref name = "Robinson">Robinson HC, Chasen FN. (1936). ''The Birds of the Malay Peninsula, Vol. 3''. HF and G Witherby, London.</ref> The legs are a dull red-flesh colour,<ref name = "Hancock"/> with the tarsi measuring 188 – 225mm.<ref name ="Robinson"/> It has long thick toes that probably serve to increase surface area of its feet and therefore reduce pressure from standing and walking on the soft mud of its foraging area, so that the bird does not sink considerably when foraging and feeding.<ref name ="Swennen">{{cite journal|vauthors=Swennen C, Marteijn EC |year= 1987|title= Notes on the feeding behaviour of the Milky Stork ''Mycteria cinerea''|journal=Forktail|volume= 3|pages= 63–66|url=http://orientalbirdclub.org/wp-content/uploads/2012/07/Swennen-MilkyStork.pdf}}</ref>

During courtship, the bill turns deep yellow, with a greyish tan on the basal third; and the legs become deep magenta. The sexes are similar, but the average male is slightly larger with a longer, thinner bill.<ref name ="Hancock"/>

The adult is readily recognisable in the field by its white head feathers, yellow-orange bill, and pink legs.<ref name = "Swennen"/> It is distinguished from other waders such as egrets and lesser adjutants by its extensively white body plumage and black wing coverts.<ref name = "Iqbal">Iqbal M. 2008. Survey and conservation of milky stork Mycteria cincerea in Sumatra Indonesia. Final report to Rufford Small Grant.</ref> However, the milky stork resembles and may therefore be confused with the partly sympatric Asian Openbill and various white egret species.<ref name = "Hancock"/> Nevertheless, the egrets are smaller and completely white, and the Asian Openbill is also smaller and distinguished from the milky stork by the grey bill.<ref name = "Hancock"/> In the northern part of its range around Vietnam, milky storks occasionally occur in sympatry with the closely related and morphologically similar painted storks.<ref name = "Hancock"/> However, the painted stork is distinguished from the milky stork in adult plumage by the former's black and white breast band and wing coverts, pink inner secondaries, more restricted bare head skin, and generally brighter soft part colouration.<ref name = IUCN/><ref name="Hancock"/>

Like other storks, the milky stork usually soars on thermals to travel between areas. Flocks of up to a dozen birds can be seen soaring on thermals at great heights between 10:00 and 14:00.<ref name="HoogerwerfSiccama">{{cite journal|vauthors=Hoogerwerf A, Siccama GF |year= 1937|title= De avifauna van Batavia en omstreken|journal=Ardea|volume=26|pages= 116–159}}</ref> At breeding colonies and feeding grounds, flight is contagious in that take-off by one bird is quickly followed by others.<ref name = "Hancock"/> Average flapping rate has been estimated at 205 beats per minute.<ref>{{cite journal|author=Kahl MP|year= 1971|title= Flapping rates of storks in level flight|url=https://sora.unm.edu/node/22122|journal= The Auk |volume=88|issue= 2|page= 428|doi= 10.2307/4083891|jstor= 4083891|doi-access= free}}</ref>

===Juvenile === At hatching, the chicks are covered with white down. Contour feathers begin to appear by 10–14 days, and the chicks become fully feathered with full plumage after 4–6 weeks.<ref name = "Hancock"/><ref name = "Hoogerwerf">{{cite journal|author=Hoogerwerf A. |year=1936|title= Met de camera naar de nimmerzatten|journal= Tropische Natur |volume=25|pages= 83–96}}</ref> This plumage is typically pale greyish brown with a white lower back, rump and tail coverts; some white downy feathers remaining under the wings and underside of the body; black wing and tail feathers with a white and dark brown wing lining; distinct feathering on the greyish brown head, and dull yellow bare parts.<ref name = IUCN/><ref name = "Hancock"/><ref name = "Elliot"/><ref name = "Hoogerwerf"/> After about 10 weeks when juveniles have fledged,<ref name = "Hoogerwerf"/> loss of head feathers begins; and the dark, bare areas on the forehead and sides of the head around the eyes become visible.<ref name = "Hancock"/><ref name = "Hoogerwerf"/> These dark bare areas are sometimes interspersed with dull orange spots.<ref name = "Hoogerwerf"/> Nestlings also have a dark brownish grey bill and skin around the bill and eye.<ref name = "Hoogerwerf"/>

By the age of three months, the previously feathered head is now completely bald and the dull bill has become warm yellow with a greenish yellow tip.<ref name = "Hancock"/><ref name = "Hoogerwerf"/> Both features are characteristic of adults. Milky stork juveniles appear almost identical to painted stork juveniles,<ref name = "Yee">{{cite journal|pmid=23846110|year=2013|last1=Yee|first1=E. Y.|title=Identification of hybrids of painted and milky storks using FTA card-collected blood, molecular markers, and morphologies|journal=Biochemical Genetics|volume=51|issue=9–10|pages=789–99|last2=Zainuddin|first2=Z. Z.|last3=Ismail|first3=A|last4=Yap|first4=C. K.|last5=Tan|first5=S. G.|doi=10.1007/s10528-013-9607-8|s2cid=254281344 |url=http://psasir.upm.edu.my/id/eprint/30206/1/Identification%20of%20hybrids%20of%20painted%20and%20milky%20storks%20using%20FTA%20card.pdf}}</ref> but are said to be distinguishable from painted stork juveniles by their paler underwing lining contrasting with the completely black flight feathers, whereas this underwing lining is completely black in painted storks.<ref name = "Hancock"/>

===Other features=== The milky stork is usually silent during non-breeding. At nests, individuals utter a falsetto "fizz" call during the Up-Down display.<ref name = "Hancock"/><ref name = "Elliot"/> The young utter a froglike croak when begging for food.<ref name = "Elliot"/>

Especially in captivity in National Zoo of Malaysia, Singapore Zoo, and Dusit Zoo, milky storks and painted interbreed to produce hybrid offspring.<ref name = "Yee"/><ref name = "Li">Li D, Wei Z, Yatim SH, Howes J, Ilias R. (2006). [http://www.wildlife.gov.my/images/stories/penerbitan/lain_lain/Milky_Stork_Report.pdf Status overview and recommendations for the conservation of milky stork ''Mycteria cinerea'' in Malaysia]. Final report of the 2004/2006 milky stork surveys in the Matang Mangrove Forest, Perak, Malaysia.</ref> These hybrids apparently vary in appearance through different combinations of milky stork and painted stork phenotypes in varying proportions.<ref name = "Yee"/><ref name = "Li"/> Because these hybrid juveniles are not readily distinguishable from pure-bred juveniles based on morphology, molecular methods have been used to detect possible hybrids.<ref name = "Yee"/> Compared to the parent painted stork, the adult hybrid has a pink rather than orange bill and head. Adult hybrids may also have some small black spots on the white wing and a subtle pink tinge on the feathers.<ref name = "Li"/>

Across all ages in this species, the iris is dark brown; and the legs are pinkish, but appear white due to a covering of the birds' excreta.<ref name = "Hoogerwerf"/>

==Distribution and habitat== thumb|Milky stork in Borneo The milky stork's range is restricted to Southeast Asia, where it is widely but patchily distributed.<ref name = "Iqbal"/> It occurs in Sumatra (its global stronghold), Java, Sulawesi, eastern Malaysia, Cambodia, southern Vietnam (where it probably largely recolonised after the war of 1963–75<ref name = "Hancock"/>), Bali, Sumbawa, Lombok and Buton.<ref name=IUCN/> It historically occurred in southern Thailand,<ref>Byers O, Brouwer K, Coulter M, Seal US. (1995). [http://www.cbsg.org/sites/cbsg.org/files/documents/Stork,%20Ibis%20and%20Spoonbill%20CAMP%20Report_1995.pdf Stork, Ibis and Spoonbill Conservation Assignment Management Plan: Working Document]. IUCN/SSC Conservation Breeding Specialist Group: Apple Valley, MN.</ref> but is now very likely extinct there.<ref>Treesucon U, Round PD. (1990). [https://www.researchgate.net/publication/39014374_Report_on_threatened_birds_in_Thailand Report on threatened birds in Thailand]. Tiger Paper 7: 1–9.</ref><ref name = "Morioka">{{cite journal|vauthors=Morioka H, Yan C |year=1990|title= A record for the Milky Stork for Thailand|journal = Japanese Journal of Ornithology|volume= 38|issue=3|pages= 149–150|doi=10.3838/jjo.38.149|doi-access=free}}</ref> One perfect adult male milky stork specimen from Setul in Peninsula Thailand taken from 1935 was later found among collections of the Zoological Reference Collection at the National University of Singapore, suggesting that the species was formerly resident here.<ref name = "Morioka"/> The discovered specimen was the first, and probably also the last milky stork to be reported from Thailand,<ref name = "Morioka"/> although this stork probably still occasionally visits Thailand as a vagrant.<ref name = IUCN/> It is also vagrant elsewhere to countries such as Bali and Sumbawa,<ref name = "SilviusVerheugt">{{cite journal|vauthors=Silvius MJ, Verheugt WJ |year= 1989|title= The status of storks, ibises and spoonbills in Indonesia|journal=Kukila|pages=119–132|issue=3–4|volume=4|url=http://kukila.org/index.php/KKL/article/view/72}}</ref> and is resident on Sumatra, Java<ref>{{Cite web|url=https://www.researchgate.net/publication/299395017|title=Milky Stork (Ibis cinereus) and birds of the Javan Plain (PDF Download Available)|website=ResearchGate|language=en|access-date=2017-11-01}}</ref> and Sulawesi (all within Indonesia). The milky stork was first reported on Sulawesi when a group of five apparently resident individuals was sighted there in 1977.<ref>{{cite journal|vauthors=Escott CJ, Holmes DA |year= 1979|title= The avifauna of Sulawesi, Indonesia: faunistic notes and additions|journal= Bulletin of the British Ornithologists' Club |volume=100|pages= 189–194}}</ref> The island of Madura may also support an important population after 170 individuals were sighted there in 1996.

The milky stork previously ranged more widely throughout Southeast Asia. For example, it was formerly widely distributed along the coasts of the Malaysian Peninsula,<ref name = "Robinson"/> but is now restricted to Matang Mangrove Forest in Perak.<ref name = "Li"/><ref name = "IsmailRahman2016">{{cite journal|vauthors=Ismail A, Rahman F |title=Current Status of the Milky Stork Re-introduction Programme in Malaysia and Its Challenges|journal=Tropical Life Sciences Research|volume=27|issue=2|pages=13–24|doi=10.21315/tlsr2016.27.2.2|pmid=27688848|pmc=5031160|year=2016}}</ref>

The milky stork is predominantly a lowland coastal species throughout its range; where it inhabits mangrove, freshwater and peat swamps, and estuaries.<ref name = "Hancock"/><ref name = "Verheugt">{{cite journal|author=Verheugt WJM|doi=10.2307/1521260 |title=Conservation status and action program for the milky stork ''Mycteria cinerea''|journal=Colonial Waterbirds |volume=10 |issue=2 |pages=211–220 |jstor=1521260 |year=1987 }}</ref> The only proven breeding records however are reported from mangroves bordering the feeding grounds.<ref name = "Elliot"/><ref name = "Verheugt"/><ref name = "DanielsenSkov1986">Danielsen F, Skov H. (1986). Observations of waterbirds along the coast of South-east Sumatra. Copenhagen, Denmark. Mimeographed.</ref> It forages on tidal mudflats, in shallow saline or freshwater pools, freshwater marshes, fishponds, rice fields; and on backswamps along river floodplains up to 15&nbsp;km from the coast.<ref name = "Elliot"/><ref name = "Verheugt"/> The milky stork's breeding habitat requirements are extensive and undisturbed mangrove (and probably also riverine or dryland) forest with tall, outstanding trees behind it; and shallow pools within the forest for juveniles to forage in.<ref name = "AllportWilson">Allport GA, Wilson S-A. (1984). Results of a census of the milky stork ''Mycteria cinerea'' in West Java: report of the Indonesian Waterbird Survey Expedition, July–October 1984. Cambridge, UK: International Council for Bird Preservation (Study Report 14), University of East Anglia.</ref> The tall trees are also used for resting, and there should be sufficient individual limbs from which to take off. With a lack of such suitable trees, manmade alternatives such as cart wheels mounted on poles have been proposed.<ref name = "AllportWilson"/>

In Peninsular Malaysia, the milky stork is more exclusively marine than the congeneric painted stork.<ref name = "Elliot"/> However, the two species' ranges are said to overlap in the marshy plains of Cambodia, where they probably use the same habitats.<ref name = "Delacour"/>

==Migration and other movements== The milky stork probably undertakes short seasonal migration outside the breeding season, but little is known of the timing and path of such movements.<ref name = "Elliot"/> Local migrations by milky storks (and several other wader species) may be caused by onset of drought in the dry season.<ref name = "Verheugt1993">{{cite journal|vauthors=Verheugt WJ, Skov H, Danielsen F |year=1993|title= Notes on the birds of the tidal lowlands and floodplains of South Sumatra Province, Indonesia|journal=Kukila|volume= 6|pages= 53–84|issue=2|url=http://kukila.org/index.php/KKL/article/view/107}}</ref> In Cambodia however, it disperses during the wet season from Tonlé Sap Lake probably to the coast.<ref name = "Elliot"/> Milky storks are reported migrating from Sumatra to Java, and across the Sunda Straits, in September and October.<ref name = "AllportWilson"/> Although these apparent migrations are not extensively mapped, milky stork flocks are reported to range over 200&nbsp;km in a day.<ref name = "AllportWilson"/>

Adults breeding on the Javan island of Pulau Rambut have also been noted to commute daily on and off the island to feed at the fishponds and rice fields on the Javan mainland.<ref name = "AllportWilson"/> The breeding colony on Pulau Rambut may also be irregularly visited by varying numbers of migrants throughout the year.<ref name = "Elliot"/>

==Behaviour and ecology==

===Breeding=== A pair of milky storks in flight in Singapore|thumb|left Breeding typically occurs after the rains during the dry season that can last from April to November.<ref name = "Hancock"/><ref name = "Verheugt1993"/> The onset of breeding can vary in timing throughout the species' range,<ref name = "Li"/> but usually lasts for three months<ref name = "Verheugt"/><ref name = "Kahl1987">{{cite journal|author=Kahl MP|year= 1987|title= An overview of the storks of the world|journal= Colonial Waterbirds |volume=10|issue= 2|pages= 131–134|doi=10.2307/1521251|jstor=1521251 }}</ref> and probably coincides with maximum fish stocks and density following fish reproduction in the rainy season.<ref name = "Hancock"/> In South Sumatra for example, the milky stork can breed June–September,<ref name = "Hancock"/><ref name = "Verheugt1993"/> and has been observed in breeding plumage in May,<ref>{{cite journal|vauthors=Nash SV, Nash AD |year= 1985|title= A checklist of the forest and forest edge birds of the Padang-Sugihan Wildlife Reserve, South Sumatra|volume= 2|journal=Kukila |issue=3|pages= 53–59|url=http://kukila.org/index.php/KKL/article/view/14}}</ref> or as early as February.<ref name = "Verheugt"/> Breeding is probably slightly earlier in Java given that eggs have been found in nests here as early as March,<ref name = "Hancock"/><ref name = "HoogerwerfSiccama"/> with one report of a clutch fledging in July (Hoogerwerf, 1936). Breeding in Java is however probably commonest July–August.<ref name = "Elliot"/> At Tonle Sap in Cambodia, egg-laying can begin in January and February where the dry season begins even earlier.<ref>Parr JW, K Eames, JC Sun Hean, Chamnan Hong, Som Han, Vi La Pich and Kim Hout Seng. (1996). ''Biological and socio-economic aspects of waterbird exploitation and natural resource utilization at Prek Toal, Tonle Sap Lake, Cambodia''. Bangkok: IUCN.</ref> In Malaysia, eggs have been found in nests exclusively in August.<ref name = "Hancock"/><ref name = "Robinson"/>

The milky stork breeds colonially in mangrove swamps, with breeding colonies ranging in size from 10–20 to a few hundred nests.<ref name = "Hancock"/> In Java, breeding colonies of 75–100 nests have been estimated to cover 4.5 ha, with 5–8 nests per tree within colonies having been recorded.<ref name = "Hoogerwerf"/> The height of the nest above the ground notably varies. Nests are commonly built in tall ''Avicennia marina'' and other ''Avicennia'' tree species in Java, and ''Rhizosphora apiculata'' trees in Sumatra, in both cases usually 6–14 m above ground,<ref name = "Verheugt"/><ref name = "DanielsenSkov1986"/><ref name = "Silvius1988">{{cite journal|author=Silvius MJ|year= 1988|title= On the importance of Sumatra's east coast for waterbirds, with notes on the Asian Dowitcher ''Limnodromus semipalmatus''|journal= Kukila |volume=3|issue=3–4|pages= 117–137|url=http://kukila.org/index.php/KKL/article/view/370}}</ref> but sometimes in the very tops of trees.<ref name = "Madoc">{{cite journal|author=Madoc GC|year= 1936|title= On the nidification of some Malayan birds|journal=Bulletin of the Raffles Museum|volume= 12|pages= 124–133}}</ref> Nests on Pulau Rambut are built in tops of outstanding mangrove trees 30 m high.<ref name = "Verheugt"/> Similar nesting characteristics were observed on the island of Pulau Dua when the species still bred there.<ref name = "Hancock"/> In Indonesia, some milky storks nest close to the ground in dense shrubs of ''Acrostichum'' mangrove ferns 2-6m above the ground.<ref name = "Li"/><ref name = "Danielsen1991b">{{cite journal|vauthors=Danielsen F, Purwoko A, Silvius MJ, Skov H, Verheugt W |year= 1991|title= Breeding colonies of milky stork in South Sumatra|journal= Kukila |volume=5|issue=2|pages=133–135|url=http://kukila.org/index.php/KKL/issue/view/15}}</ref> Milky storks also commonly nest in dead or dying mangrove trees.<ref name = "Li"/> Further, some colonies in South Sumatra have been located far inland at brackish lakes or freshwater swamps in Alstonia trees reaching up to 60 m high.<ref name = "Silvius1988"/>

The nests are sturdy, bulky structures measuring about 50&nbsp;cm in diameter and predominantly comprising medium live sticks of ''Avicenna'' species on which many leaves are still attached.<ref name = "HoogerwerfSiccama"/><ref name = "Li"/><ref name = "Madoc"/> These nests resemble those of the grey heron and the white ibis but are slightly more robust and comprise thicker twigs.<ref name = "HoogerwerfSiccama"/><ref name = "Hoogerwerfb">{{cite journal|author=Hoogerwerf A.|year= 1936|title= On the nidification of some Javan birds|journal= Bulletin of the Raffles Museum |volume=12|pages= 118–124}}</ref> However, other nests found have been small and flimsy structures that resemble those of doves.<ref name = "Hoogerwerfb"/> When collecting nesting material, milky storks break off live branches from trees by grasping the branch with their bill and flying upwards a short distance, which appears to be a difficult task and sometimes unsuccessful.<ref name = "HoogerwerfSiccama"/><ref name = "Hoogerwerf"/> If the stork does not manage the free the branch, it moves on to another one. Nest building continues even with young in the nest.<ref name = "Hoogerwerf"/>

Clutch sizes range from 1–4 eggs,<ref name = "Elliot"/> but 2–3 eggs are typical.<ref name = "Hoogerwerf"/><ref name = "Verheugt"/> Egg dimensions measure 59.0–74.5&nbsp;mm in length and 43.0–48.0&nbsp;mm in width, are relatively small compared to the adult body size, and resemble those of ''Leptoptilos javanicus'', but are slightly paler. The incubation period is estimated at 27–30 days. Several days can elapse between the hatching of the first and last egg, so that the oldest and youngest chicks differ considerably in size. The clutch is alternately brooded by the male and female. When parents exchange nest duties, the returning parent and brooding parent greet each other with loud, rapid bill clattering, accompanied by deep head bowing and neck stretching.<ref name = "Hoogerwerfb"/> In response to disturbances at the nest, the brooding bird gives an arching display that typically resembles that in other ''Mycteria'' species.<ref name = "Hancock"/><ref name = "Hoogerwerfb"/>

Courtship consists of repeated bowing and bill-raising from both partners, who stand opposite each other and perform this display in a mirror action.<ref name = "Silvius1988"/> Many displays at the nest resemble those of other ''Mycteria'' species. The male at the nest advertises to the arriving female using display preening, whereupon the female responds with a balancing posture and gaping. An up-down greeting display from both partners follows the arrival of one partner at the nest, and the male adopts a flying-around display upon female arrival. Both partners at the nest retract the skin of their head to expose two or three times as much bare skin as between displays when the skin hangs loosely.<ref name = "Hancock"/>

In South Sumatra, it is found to breed alongside lesser adjutants, black-headed ibis, and various heron species.<ref name = "Danielsen1991b"/> In Cambodia, milky storks have been reported breeding alongside painted storks, lesser adjutants, and spot-billed pelicans in flooded forest around Tonle Sap during the early dry season in January and February. Colonies here are situated in mangrove backswamps 1–4&nbsp;km from the coast in dense ''Archostichum'' ferns or dead trees.<ref name = "Danielsen1991b"/>

Breeding in Malaysia is probably at best scarce and unsuccessful.<ref name = "Li"/> Several adult storks were observed in breeding plumage at Kuala Gula in July 1984, and about 20 nests were reported there in 1989 together with an increasing adult population.<ref name = "Hancock"/> Before these observations, signs of breeding in this species had not been recorded since 1935.<ref name = "Madoc"/> However, no juveniles have been seen in Malaysia since 1983, and the apparent lack of breeding success has probably been due to high predation pressure.<ref name = "Li"/> Breeding no longer occurs on the Javan Island of Pulau Dua. Since the mid-1970s, this island has been connected with the Javan mainland through rapid coastal accretion; whereupon easy human access led to large-scale deforestation for firewood harvest. Breeding ceased due to removal of suitable nesting habitat of tall trees.<ref name = "Verheugt"/> However, individuals have still been seen on the island in courtship and there have been suggestions that the breeding status could be restored here through rigorous conservation measures.<ref name = "AllportWilson"/> Some breeding still occurs on Pulau Rambut; a few breeding pairs were observed here at Jakarta Bay in 2014.<ref name=IUCN/>

Young captive milky storks can become sexually mature from three months of age,<ref name = "Yaacob">{{cite journal|author=Yaacob MN |doi=10.1111/j.1748-1090.1994.tb03553.x|title= Captive-breeding and reintroduction project for the milky stork ''Mycteria cinerea'' at Zoo Negara, Malaysia|journal=International Zoo Yearbook|volume=33|pages=39–48|year=2007}}</ref> but breeders at this age appear precocious and inexperienced; so that actual breeding age is probably slightly older.<ref name = "Yaacob"/> In its natural habitat, young storks begin to leave their natal breeding grounds at 3–4 months of age.<ref name = "Hoogerwerf"/> Especially in captivity, the milky stork is further found to occasionally breed with the painted stork.<ref name = "Yee"/><ref name = "Li"/> One hybrid of a male lesser adjutant and female milky stork was also hatched at Jurong Bird Park, Singapore.<ref name = "Li"/>

===Food and feeding=== The milky stork's diet is diverse.<ref name = "Elliot"/> In Malaysia, the core of the diet appears to comprise mudskippers of ''Periophthalmus'' and Gobiidae 10–23&nbsp;cm long;<ref name = "Swennen"/><ref name = "Li"/> although catfish ''Arius'' spp. may be a main dietary component in South Sumatra.<ref name = "Iqbal"/> Other prey recorded from South Sumatra include milkfish, giant mudskipper (''Periophthalmodon schlosseri''), mullet species of Moolgards and ''Chelon'',<ref name="Iqbal" /> eel catfish ''(Plotosus canius''), fourfinger threadfin (Eleutheronema tetradactylum), and Chinese silver pomfret (''Pampus chinesis'').<ref name="Elliot" /> Snakes and frogs are reportedly also taken for food,<ref name="Elliot" /> especially to feed to young.<ref name="HoogerwerfSiccama" /> Parents feed nestlings large fishes, eels, and mudskippers up to 20&nbsp;cm long.<ref name="Hoogerwerf" /> In Sumatra, the elongate mudskipper (''Pseudapocryptes elongates'') was the most common prey found in nests<ref name="IUCN" .<ref /><ref name="Iqbal" /> Other prey found in nests include the Indian prawn (''Fenneropenaeus indicus)'' and one clupeid fish species (''Thryssa dussumieri'').<ref name = "Iqbal"/>

The young eat voraciously; small young up to two weeks old can be fed by the parent bird up to four times in two hours, but older young less often.<ref name = "Hoogerwerf"/> Because feeding begins before all young have hatched, the youngest (and smallest) chicks are competitively disadvantaged and commonly die of starvation, especially since the parent bird does not appear to distribute food equally among the brood.<ref name = "Hoogerwerf"/> At high temperatures, adults sometimes bring water to the nest and drool it from their bills over the nestlings for cooling and drinking.<ref name = "Hancock"/>

Milky storks also appear to exploit commercial shrimp as food. Active shrimp ponds usually last for three months before drying, whereupon remaining shrimp are exposed on the bottom as water level recedes, and milky stork and other waders come to feed on the remaining shrimps.<ref name = "IsmailRahman2016"/> Such a feeding advantage could become increasingly available as land-based aquaculture expands in Kuala Gula.<ref name = "IsmailRahman2016"/> In Java, they are also reported to feed at fishponds, especially after the dry season when waters have receded to uncover mud expanses suitable for their feeding.<ref name = "WilsonAllport">Allport GA, Wilson S-A. (1984). Results of a census of the milky stork Mycteria cinerea in West Java: report of the Indonesian Waterbird Survey Expedition, July–October 1984. Cambridge, UK: International Council for Bird Preservation (Study Report 14), University of East Anglia</ref> These manmade environments may however disfavour breeding.<ref name = "IsmailRahman2016"/>

The milky stork's daily food intake has been estimated at 630 g wet weight, which may be able to be met within two hours at maximum foraging intensity.<ref name = "Swennen"/> Various feeding mechanisms have been noted in this stork. However, as in other ''Mycteria'', the milky stork locates and captures prey predominantly by sense of touch,<ref name = "Kahl1972"/><ref name = "Swennen"/> usually by bill groping or direct bill probing.<ref name = "Indrawan">{{cite journal|author=Indrawan M, Lawler W, Widodo W, Sutandi|year= 1993|title= Notes on the feeding behaviour of milky storks ''Mycteria cinerea'' at the coast of Indramaya, west Java|journal=Forktail|volume= 8|pages= 143–144|url=http://orientalbirdclub.org/wp-content/uploads/2012/09/Indrawan-MilkyStork.pdf}}</ref> Because food location is primarily tactile, foraging is most efficient at high prey concentrations.<ref name = "Kahl1987"/> The groping method consists of walking slowly through shallow water with the partially open bill submerged about three quarters in the water.<ref name = "Silvius1988"/> The stork rapidly shuts its mandibles when a prey item touches the groping till, raises its head and quickly swallows the item whole after some tossing.<ref name = "Kahl1972"/><ref name = "Swennen"/><ref name = "AllportWilson"/> After swallowing a large fish, the stork may rest for up to one minute before resuming foraging.<ref name = "Swennen"/> Alternatively, the bird may stand passively at the water's edge with its half-open bill steadily submerged in the water where waves are present, so that water flows through the bird's mandibles.<ref name = "Silvius1988"/> The milky stork also sometimes draws its bill through the water in an arc side-to-side when standing or walking, until the bill touches a prey item.<ref name = "Li"/>

Another common tactile feeding method in this stork is direct probing of its bill around deep holes in the mud.<ref name = "Swennen"/> With partially open mandibles, the bird inserts and partially withdraws its bill from the mud for 5–32 seconds per hole. The bill is often inserted into the mud three quarters up the bill length, but sometimes along the full or up to the eyes.<ref name = "Swennen"/> Other foraging methods observed in this stork are prey herding mechanisms typical of other ''Mycteria'' species.<ref name = "Kahl1972"/> One of these is foot stirring, whereby the stork stands on one leg and disturbs the river bed with the foot of the opposite leg; which may drive aquatic prey from places inaccessible to the storks.<ref name = "AllportWilson"/> Milky storks also forage in flocks at high prey density, whereby they cooperatively flush fish in shallow water to divert them to their half-open bills; as has been observed in Java.<ref name = "Indrawan"/> Milky storks also often feed in aggregations alongside other wading bird species such as lesser adjutant and egrets.<ref name = "Verheugt"/> This stork occasionally detects aquatic prey by direct visual searching.<ref name = "Elliot"/><ref name = "Swennen"/><ref name = "Indrawan"/>

During and after the local rainy season, which lasts from November to March, individuals apparently forage in great numbers in the inundated rice fields; and lower numbers of individuals observed at the coast may reflect the more favourable feeding conditions further inland.<ref name = "Verheugt"/> Sightings have been regularly reported along the Batang Hari River 50&nbsp;km from the coast.<ref name = "Verheugt"/> During breeding, juveniles commonly forage near the breeding colony in shallow mangrove pools with high fish density.<ref name = "AllportWilson"/>

===Other behavior=== During high tide, individuals often roost in mangrove trees or in remnant trees on rice fields.<ref name = "Verheugt1993"/><ref>{{cite journal|vauthors=Danielsen F, Skov H |year=1987|title= Waterbird survey results from south east Sumatra|journal= Oriental Bird Club Bulletin |volume=6|pages= 8–11}}</ref> Roosting also occurs in crowns of tall mangrove trees<ref name = "Hancock"/> and on the ground on intertidal mudflats and marshes.<ref name = "Li"/> Between foraging activities, individuals have been observed standing in shaded spots or in the sun adopting a wings drooped position.<ref name = "AllportWilson"/>

Common comfort movements in the milky stork include allopreening between breeding partners and head shaking. Individuals perched near incubating partners also carrying out head rubbing, whereby the stork oils the bare head skin on its preen gland and then rubs its head on its plumage.<ref name = "Hancock"/>

==Threats and survival== The global milky stork population has been declining substantially, especially from the late 1980s, and has been largely attributable to habitat destruction and disturbance through mangrove deforestation for human activities such as fish farming, tidal rice cultivation,<ref name = "Hancock"/> timber exploitation,<ref name = "Verheugt"/> and in Indonesia, human resettlement.<ref>{{cite journal|author=Luthin CS|doi=10.2307/1521258 |year= 1987|title =Status of and conservation priorities for the world's stork species|journal=Colonial Waterbirds |volume=10 |issue=2 |pages=181–202 |jstor=1521258 }}</ref> Deforestation has led to a lack of suitable mature trees for the species to nest in and thereby affected breeding success.<ref name = "Li"/> Breeding colonies have also declined through increased illegal international trade in this bird from the mid-1980s<ref name = "Verheugt"/><ref name = "Danielsen1991">{{cite journal|vauthors=Danielsen F, Skov H, Suwannan U |year= 1991|title= Breeding colonies of waterbirds along the coast of Jambi Province, Sumatra, August 1989|journal= Kukila |volume=5|issue=2 |pages=135–137|url=http://kukila.org/index.php/KKL/issue/view/15}}</ref> and, especially in South Sumatra, poaching of eggs and juveniles for human consumption.<ref name = "Iqbal"/> Juveniles in particular have been sold to and purchased by zoos in Singapore, Kuala Lumpur, Brunei, and several European zoos.<ref name = "Danielsen1991"/> The milky stork is said to be generally vulnerable to human disturbance,<ref name = "Verheugt"/> which may also explain the marked widespread decline of this species. Although fishponds and shrimp farms, for example, can provide additional feeding grounds and therefore allow feeding opportunism for this species, presence of these manmade structures can disturb nearby breeding and therefore affect the population in the long term.<ref name = "IsmailRahman2016"/>

The milky stork was essentially eliminated from Vietnam through widespread destruction of mangrove swamps during the Southeast Asian War in 1963–75.<ref name = "Hancock"/><ref name = "Verheugt"/> Subsequent large-scale reforestation may however have led to some recolonization;<ref name = "Verheugt"/> although the species has also suffered long-term effects of herbicide application in Southern Vietnam in later years.<ref name = "Verheugt"/>

This stork has various natural predators. In South Sumatra, monitor lizards, especially ''Varanus salvator'', have been reported to predate milky stork eggs and juveniles.<ref name = "Iqbal"/> Crocodiles ''(Crocodilus porosus)'' also sometimes eat young milky storks.<ref name = "Iqbal"/> In Matang Mangrove Forest in Malaysia, brahminy kites, water monitor lizards, and common palm civets ''(Paradoxurus hermaphroditus)'' are potential (nest) predators and probably contribute to low survival here.<ref name = "Li"/> In captivity in Malaysia, the milky stork may also be potentially threatened by the crab-eating macaque (''Macaca fascicularis''), which is a potential predator of stork eggs and chicks, and whose range has gradually expanded here. This monkey could swim across to nest sites surrounded by water, as they have done for captive grey herons.<ref name = "Yaacob"/> On Pulau Rambut, potential predators include reticulated python, cat snakes (especially ''Boiga dendrophila),'' and Brahminy kite.<ref name = "Iqbal"/> White bellied sea eagle ''Haliaeetus leucogaster'' and monitor lizard are also reported to predate chicks here.<ref>Imanudin A, Mardiastuti A. (2003). Ekologi bangau bluwok Mycteria cinerea di Suaka Margasatwa Pulau Rambut, Jakarta. Fakultas Kehutanan IPB/Disney Wildlife Conservation/Wildlife Trust.</ref>

Another potential threat to the milky stork is contamination of its natural habitat with elevated concentrations of ions of metals such as copper, zinc and lead. Sources of this observed contamination include use of agrochemicals in Kuala Gula, corrosion and runoff from jetties and boats coated with these metals, and aquaculture development.<ref>{{cite journal|doi=10.1080/02772248.2014.892941|title=Metals contamination in the foraging area of Milky Stork: Evidence of anthropogenic inputs in the aquatic environment of Kuala Gula, Malaysia|journal=Toxicological & Environmental Chemistry|volume=95|issue=9|page=1499|year=2014|last1=Rahman|first1=Faid|last2=Ismail|first2=Ahmad|last3=Yusof|first3=Shahrizad|s2cid=97835086 }}</ref> On Pulau Rambut, breeding colonies might also be threatened by increasing sea pollution.<ref name = "Verheugt"/>

Population recovery for this species has relied largely on captive breeding. In 1987, the first captive breeding and reintroduction project for the milky stork was initiated in Zoo Negara in Malaysia (a country where the wild milky stork population declined by over 90% from the 1980s to 2005<ref name = "Li"/>) from a small young group of five males and five females received from Singapore Zoo and Johor Zoo.<ref name = "Yaacob"/><ref name = "IsmailRahman2012">{{cite journal|vauthors=Ismail A, Rahman F |year=2012|title= An urgent need for milky stork study in Malaysia|journal= Tropical Agricultural Science |volume=35|issue=3|pages= 407–412|url=http://www.pertanika.upm.edu.my/Pertanika%20PAPERS/JTAS%20Vol.%2035%20(3)%20Aug.%202012/02%20pg%20407-412.pdf}}</ref> From these 10 individuals, the captive population increased to over 100 individuals by 2005.<ref name = "IsmailRahman2012"/> Therefore, with the decline in the wild milky stork population in Malaysia since the 1980s, the captive, free-flying population has steadily risen.

The first successful milky stork reintroduction was carried out in Kuala Selangor Nature Park in 1998 with the release of 10 captive-bred individuals here.<ref name = "IsmailRahman2016"/> Matang Mangrove Forest in Malaysia has been a popular candidate reintroduction site because this area is considered a suitable milky stork habitat in terms of shelter, breeding and feeding grounds; and there are apparently minimal threats from predators and parasites.<ref name = "IsmailRahman2012"/> The area is also protected and systematically managed, and raw materials are sustainably harvested here.<ref name = "IsmailRahman2012"/> However, captive individuals released into their natural habitat face new potential threats such as susceptibility to disease, lack of ability to hunt for food and defend territory, and lack of ability to effectively detect and evade potential predators.<ref name = "IsmailRahman2012"/> These released individuals may also harbour disease and parasites that could harm wild populations.<ref name = "Li"/>

Particularly for captive individuals, there is the risk of a loss of genetic integrity through hybridization with painted storks in captivity<ref name = "Yee"/><ref name = "Li"/> or in the wild in the northern parts of the milky stork range where it may co-occur with the painted stork.

Where successful, conservation of this species in the wild has relied on maintaining an integrated network of wetland preserves, as has been done in reforestation and protection schemes in Vietnam that may have led to some recolonization by the species.<ref name = "Hancock"/> Raising public awareness for this species and its threatened status has also been identified as an indispensable action for successful conservation.<ref name = "Iqbal"/>

==In culture and relationship to humans== The milky stork is well known among Indonesian locals and is readily distinguished by them in the field from other waders; although it has at least historically been commonly (and sometimes illegally) harvested for meat and eggs.<ref name = "Iqbal"/> Like many other wading bird species, the milky stork is also sometimes considered a minor pest in the aquaculture industry by feeding on commercial fish and shrimps.<ref name = "IsmailRahman2016"/><ref>Kushlan JA, Hafner H. (2000). ''Heron Conservation''. San Diego, California: Academic Press.</ref> This stork is however officially protected in Malaysia and Indonesia<ref name = "Verheugt"/> and has been listed on Appendix I of CITES since 1987.<ref name = "Hancock"/>

This stork has occasionally appeared in zoos such as Vienna Zoo and Washington Park Zoo, with the latter having held the longest living milky stork specimen, which lived for 12 years, 4 months and 18 days (1937–1950).<ref name = "Brouwer">{{cite journal|doi=10.1111/j.1748-1090.1991.tb02376.x|title=Longevity and breeding records of storks Ciconiidae in captivity|journal=International Zoo Yearbook|volume=31|pages=131–139|year=1992|last1=Brouwer|first1=Koen|last2=Jones|first2=Marvin L.|last3=King|first3=Catherine E.|last4=Schifter|first4=Herbert}}</ref> Many juvenile zoo specimens have been misidentified as young painted storks on purchase, and later proved to be milky storks.<ref name = "Hancock"/><ref name = "Brouwer"/> The only zoos which are recorded as having bred the species are Zoo Negara (where the stork bred in captivity for the first time in 1987),<ref name = "Yaacob"/><ref name = "IsmailRahman2012"/> San Diego Zoo and Singapore Zoo.<ref name = "Brouwer"/> Captive breeding and reintroduction programmes for this stork have been widely supported by government and non-government agencies such as Perhilitan, the Malaysian Nature Society, and the Malaysian Zoological Society.<ref name = "IsmailRahman2012"/>

A milky stork in flight features on the logo of Sembilang National Park. It has also commonly appeared on calendars and posters in public awareness campaigns in Sumatra.<ref name = "Iqbal"/>

==Status== In 2023, the global population was estimated to be between 1,200–1,850 mature individuals, a reduction from approximately 5,000 in the 1980s.<ref name = "IUCN"/><ref name = "SilviusVerheugt"/> In Malaysia, population counts decreased steadily from over 100 individuals in 1984 to less than 10 by 2005 (by over 90%),<ref name = "Li"/> so that the population here faces local extinction.<ref name = "Li"/> Of the current world population estimate, almost all milky storks live in Indonesia. There are probably about 800–1,600 individuals in Sumatra, approximately 100–200 between populations on Java and Sulawesi, and few, if any, remaining in breeding populations on the southeast Asian mainland.<ref name=IUCN/> The Cambodian population is very small, numbering 100–150 individuals; and although it may be relatively stable, rapid declines are expected if serious threats persist.{{cn|date=April 2026}} Due to the substantial population declines across its range, the milky stork's population status was elevated to Endangered from Vulnerable in 2013 by the IUCN.<ref name=IUCN/>

==References== {{Reflist|30em}}

== External links == {{Commons category|Mycteria cinerea}} {{Wikispecies|Mycteria cinerea}} *[http://www.birdlife.org/datazone/species/index.html?action=SpcHTMDetails.asp&sid=3825&m=0 Species factsheet] – BirdLife International

{{Storks}} {{Taxonbar|from=Q731308}}

Category:Mycteria Category:Birds of Southeast Asia Category:Birds of Indonesia Category:Birds of Malaysia Category:Birds of Cambodia Category:Birds described in 1822