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 tall, with a wingspan of and a tail around . 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). 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.
Description Adult This medium stork stands 91–97 cm tall, making it slightly smaller than the closely related painted stork.Hancock JA, Kushlan JA, Kahl, MP. (1992). Storks, Ibises and Spoonbills of the World. Academic Press. The adult plumage is completely white except for black flight feathers of the wing and tail, which also have a greenish gloss. Wing length measures 435–500 mmDelacour J, Jabouille P. (1931).Les oiseaux de I'Indochine Francaise, 1–4. Paris: Exposition Coloniale Internationale.Kuroda N. (1936). Birds of the Island of Java. Tokyo. and the tail measures 145–170 mm. The extensive white portion of the plumage is completely suffused with a pale creamy yellow during the breeding season, hence the term "milky". This creamy tint is absent from the plumage during breeding.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. The wing coverts and back feathers are paler and have an almost white terminal band.
The bare facial skin is greyish or dark maroon; with black, irregular blotches. 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. Soon after courtship, the facial skin fades to paler orange-red. Breeding birds also show a narrow pinkish band of bare skin along the underside of the wing.
The downcurved bill is dull pinkish yellow and sometimes tipped white. The culmen length measures 194 – 275mm.Robinson HC, Chasen FN. (1936). The Birds of the Malay Peninsula, Vol. 3. HF and G Witherby, London. The legs are a dull red-flesh colour, with the tarsi measuring 188 – 225mm. 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.
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.
The adult is readily recognisable in the field by its white head feathers, yellow-orange bill, and pink legs. It is distinguished from other waders such as egrets and lesser adjutants by its extensively white body plumage and black wing coverts.Iqbal M. 2008. Survey and conservation of milky stork Mycteria cincerea in Sumatra Indonesia. Final report to Rufford Small Grant. However, the milky stork resembles and may therefore be confused with the partly sympatric Asian Openbill and various white egret species. 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. In the northern part of its range around Vietnam, milky storks occasionally occur in sympatry with the closely related and morphologically similar painted storks. 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.
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. At breeding colonies and feeding grounds, flight is contagious in that take-off by one bird is quickly followed by others. Average flapping rate has been estimated at 205 beats per minute.
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. 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. After about 10 weeks when juveniles have fledged, loss of head feathers begins; and the dark, bare areas on the forehead and sides of the head around the eyes become visible. These dark bare areas are sometimes interspersed with dull orange spots. Nestlings also have a dark brownish grey bill and skin around the bill and eye.
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. Both features are characteristic of adults. Milky stork juveniles appear almost identical to painted stork juveniles, 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.
Other features The milky stork is usually silent during non-breeding. At nests, individuals utter a falsetto "fizz" call during the Up-Down display. The young utter a froglike croak when begging for food.
Especially in captivity in National Zoo of Malaysia, Singapore Zoo, and Dusit Zoo, milky storks and painted interbreed to produce hybrid offspring.Li D, Wei Z, Yatim SH, Howes J, Ilias R. (2006). 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. These hybrids apparently vary in appearance through different combinations of milky stork and painted stork phenotypes in varying proportions. Because these hybrid juveniles are not readily distinguishable from pure-bred juveniles based on morphology, molecular methods have been used to detect possible hybrids. 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.
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.
Distribution and habitat
The milky stork's range is restricted to Southeast Asia, where it is widely but patchily distributed. 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), Bali, Sumbawa, Lombok and Buton. It historically occurred in southern Thailand,Byers O, Brouwer K, Coulter M, Seal US. (1995). Stork, Ibis and Spoonbill Conservation Assignment Management Plan: Working Document. IUCN/SSC Conservation Breeding Specialist Group: Apple Valley, MN. but is now very likely extinct there.Treesucon U, Round PD. (1990). Report on threatened birds in Thailand. Tiger Paper 7: 1–9. 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. The discovered specimen was the first, and probably also the last milky stork to be reported from Thailand, although this stork probably still occasionally visits Thailand as a vagrant. It is also vagrant elsewhere to countries such as Bali and Sumbawa, and is resident on Sumatra, Java 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. 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, but is now restricted to Matang Mangrove Forest in Perak.
The milky stork is predominantly a lowland coastal species throughout its range; where it inhabits mangrove, freshwater and peat swamps, and estuaries. The only proven breeding records however are reported from mangroves bordering the feeding grounds.Danielsen F, Skov H. (1986). Observations of waterbirds along the coast of South-east Sumatra. Copenhagen, Denmark. Mimeographed. 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 km from the coast. 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.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. 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.
In Peninsular Malaysia, the milky stork is more exclusively marine than the congeneric painted stork. However, the two species' ranges are said to overlap in the marshy plains of Cambodia, where they probably use the same habitats.
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. Local migrations by milky storks (and several other wader species) may be caused by onset of drought in the dry season. In Cambodia however, it disperses during the wet season from Tonlé Sap Lake probably to the coast. Milky storks are reported migrating from Sumatra to Java, and across the Sunda Straits, in September and October. Although these apparent migrations are not extensively mapped, milky stork flocks are reported to range over 200 km in a day.
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. The breeding colony on Pulau Rambut may also be irregularly visited by varying numbers of migrants throughout the year.
Behaviour and ecology
Breeding