Milky Stork

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 91–97 cm (36–38 in) tall, with a wingspan of 43.5–50 cm (17.1–19.7 in) and a tail around 14.5–17 cm (5.7–6.7 in). 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.

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, but is now very likely extinct there. 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. 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. 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.

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, but is now very likely extinct there. 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. 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. 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.

The milky stork's diet is diverse. In Malaysia, the core of the diet appears to comprise mudskippers of Periophthalmus and Gobiidae 10–23 cm long; although catfish Arius spp. may be a main dietary component in South Sumatra. Other prey recorded from South Sumatra include milkfish, giant mudskipper (Periophthalmodon schlosseri), mullet species of Moolgards and Chelon, eel catfish (Plotosus canius), fourfinger threadfin (Eleutheronema tetradactylum), and Chinese silver pomfret (Pampus chinesis). Snakes and frogs are reportedly also taken for food, especially to feed to young. Parents feed nestlings large fishes, eels, and mudskippers up to 20 cm long. In Sumatra, the elongate mudskipper (Pseudapocryptes elongates) was the most common prey found in nests Other prey found in nests include the Indian prawn (Fenneropenaeus indicus) and one clupeid fish species (Thryssa dussumieri). 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. 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. At high temperatures, adults sometimes bring water to the nest and drool it from their bills over the nestlings for cooling and drinking. 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. Such a feeding advantage could become increasingly available as land-based aquaculture expands in Kuala Gula. 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. These manmade environments may however disfavour breeding. 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. 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, usually by bill groping or direct bill probing. Because food location is primarily tactile, foraging is most efficient at high prey concentrations. The groping method consists of walking slowly through shallow water with the partially open bill submerged about three quarters in the water. 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. After swallowing a large fish, the stork may rest for up to one minute before resuming foraging. 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. 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. Another common tactile feeding method in this stork is direct probing of its bill around deep holes in the mud. 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. Other foraging methods observed in this stork are prey herding mechanisms typical of other Mycteria species. 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. Milky storks also forage in flocks at high prey density, whereby they cooperatively flush fish in shallow…

During high tide, individuals often roost in mangrove trees or in remnant trees on rice fields. Roosting also occurs in crowns of tall mangrove trees and on the ground on intertidal mudflats and marshes. Between foraging activities, individuals have been observed standing in shaded spots or in the sun adopting a wings drooped position. 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.

Breeding typically occurs after the rains during the dry season that can last from April to November. The onset of breeding can vary in timing throughout the species' range, but usually lasts for three months and probably coincides with maximum fish stocks and density following fish reproduction in the rainy season. In South Sumatra for example, the milky stork can breed June–September, and has been observed in breeding plumage in May, or as early as February. Breeding is probably slightly earlier in Java given that eggs have been found in nests here as early as March, with one report of a clutch fledging in July (Hoogerwerf, 1936). Breeding in Java is however probably commonest July–August. At Tonle Sap in Cambodia, egg-laying can begin in January and February where the dry season begins even earlier. In Malaysia, eggs have been found in nests exclusively in August. The milky stork breeds colonially in mangrove swamps, with breeding colonies ranging in size from 10–20 to a few hundred nests. 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. 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, but sometimes in the very tops of trees. Nests on Pulau Rambut are built in tops of outstanding mangrove trees 30 m high. Similar nesting characteristics were observed on the island of Pulau Dua when the species still bred there. In Indonesia, some milky storks nest close to the ground in dense shrubs of Acrostichum mangrove ferns 2-6m above the ground. Milky storks also commonly nest in dead or dying mangrove trees. 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. The nests are sturdy, bulky structures measuring about 50 cm in diameter and predominantly comprising medium live sticks of Avicenna species on which many leaves are still attached. These nests resemble those of the grey heron and the white ibis but are slightly more robust and comprise thicker twigs. However, other nests found have been small and flimsy structures that resemble those of doves. 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. 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. Clutch sizes range from 1–4 eggs, but 2–3 eggs are typical. Egg dimensions measure 59.0–74.5 mm in length and 43.0–48.0 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. In response to disturbances at the nest, the brooding bird gives an arching display that typically resembles that in other Mycteria species. Courtship consists of repeated bowing and bill-raising from both partners, who stand opposite each other and perform this display in a mirror action. 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 t…

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, timber exploitation, and in Indonesia, human resettlement. Deforestation has led to a lack of suitable mature trees for the species to nest in and thereby affected breeding success. Breeding colonies have also declined through increased illegal international trade in this bird from the mid-1980s and, especially in South Sumatra, poaching of eggs and juveniles for human consumption. Juveniles in particular have been sold to and purchased by zoos in Singapore, Kuala Lumpur, Brunei, and several European zoos. The milky stork is said to be generally vulnerable to human disturbance, 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. The milky stork was essentially eliminated from Vietnam through widespread destruction of mangrove swamps during the Southeast Asian War in 1963–75. Subsequent large-scale reforestation may however have led to some recolonization; although the species has also suffered long-term effects of herbicide application in Southern Vietnam in later years. This stork has various natural predators. In South Sumatra, monitor lizards, especially Varanus salvator, have been reported to predate milky stork eggs and juveniles. Crocodiles (Crocodilus porosus) also sometimes eat young milky storks. 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. 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. On Pulau Rambut, potential predators include reticulated python, cat snakes (especially Boiga dendrophila), and Brahminy kite. White bellied sea eagle Haliaeetus leucogaster and monitor lizard are also reported to predate chicks here. 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. On Pulau Rambut, breeding colonies might also be threatened by increasing sea pollution. 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) from a small young group of five males and five females received from Singapore Zoo and Johor Zoo. From these 10 individuals, the captive population increased to over 100 individuals by 2005. 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. 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 appare…

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.