Storm's Stork

Identification

This medium-sized stork stands at 75–91 cm tall and most of the plumage is black. The undertail coverts and the back of neck are white with a black cap. It has orange facial skin with a yellow ring surrounding the eye, a red iris, and a pinkish-red bill. On some but not all male individuals, the culmen of the bill is slightly concave with a basal knob.<p>The legs and feet of adults are dull red, but usually appear paler because they are often covered with the birds’ excreta. The bill and other soft body parts darken in the breeding season. The sexes are similar in appearance, but as in all storks, the male appears slightly larger. It is also speculated from field observations that the male's black cap, chest and throat are slightly glossier.<p>The plumage of the chicks at 1–3 days old is completely white, accompanied by a black crown and a black bill with a yellow-orange tip. The legs, facial skin and gular pouch are initially light yellow; as the chicks age, the legs become pink, and the facial skin becomes dark grey. The iris is initially brown.<p>The chicks grow very fast, doubling in new-born size in just under a month. By this time, they have also begun to develop black feathers on their wings, throats and bodies. After 30 days, the areas of black feathering have increased, and the black chest and wing coverts are streaked with glossy green and bronze-red. After 45 days, the young resemble adults, but they are still smaller with shorter, dark-tipped bills and paler skin colourations, and the blackness of their plumage is slightly duller. The chicks become fully feathered after 52–57 days. Wild young have been reported to leave the nest after about 60 days, and individuals in captivity can usually fly after 90 days.<p>The adult birds are generally silent outside the breeding season; however, during the breeding season they utter vocalisations that have been transcribed as "Kurau". In captivity, one adult individual was heard making a quiet sibilant whistling. Chicks have been heard to make a relatively loud froglike begging call when parents return to the nest with food.

Taxonomy

This stork was first described by Blasius in 1896, and named after the German sea captain Hugo Storm, a collector of zoological specimens in the East Indies. In Thailand, it is known as "nok kra su um", which refers to the birds’ fishing procedure by stalking along the bank of a stream in dense forest.<p>This species is very similar and closely related to the woolly-necked stork whose range partially overlaps with that of Storm's stork. Although Storm's stork has long been considered a separate species, it has also been previously treated as a subspecies of the woolly-necked stork in the more recent past. However, Storm's stork is characterised by a yellowish-orange facial skin patch around the eye that is absent in the woolly-necked stork; and the neck is black and white, whereas it is completely white in the woolly-necked stork. However, the specific distinguishing features of Storm's stork have been poorly known in the past, which in the field has frequently led to confusion with the woolly-necked stork.<p>These two species are also ecologically segregated, with Storm's stork keeping to dense forests and the woolly-necked stork mainly inhabiting open swamp, rice paddy, grassland and dry cultivated areas. There is evidence of sympatry of these two species in Sumatra, where both of these habitats are present. Further, phylogenetic analyses of the Ciconiidae based on a portion of cytochrome oxidase b gene have suggested with strong support that Storm's stork and the woolly-necked stork are sister species.

Scientific name

Ciconia stormi

Authority

(Blasius, W, 1896)

Order

Ciconiiformes

Family

Ciconiidae

Genus

Ciconia

Range and habitat

The bulk of the world population of this stork occurs on Borneo; occurring in Kalimantan (Indonesia), Swarak, Sabah (Malaysia) and Brunei. It is also found throughout Sumatra, although its range there was previously considered to be restricted to the south east. Despite being widespread on both of these islands, the population occurs at low densities and only one or a few individuals have ever been sighted together, with the largest number being 12 during an observation in Brunei. Smaller numbers live in some parts of peninsular Malaysia, where it appears to be particularly rare. An even smaller minority lives in the extreme south of Thailand, but this stork very unlikely occurs elsewhere in Thailand due to the near absence of remaining suitable habitat.<p>In 1986, the first nest of this species ever known to science was discovered in Southern Thailand. However, the construction of the Chiew Larn Dam in the same year led to destruction of much of this stork's lowland forest habitat through extensive flooding. Following the flooding, Storm's stork was therefore believed to no longer breed there and since then was previously considered extinct in Thailand. However, this stork was re-sighted in Southern Thailand in 2004 with infrared camera traps; but continues to be exceptionally uncommon given that usually only one individual has been sighted at a time despite the high intensity of camera trapping. Nevertheless, its persistence in Southern Thailand does suggest the presence of a small breeding population.<p>This stork's habitat is primarily dense lowland riverine forest and peat swamp forest, at altitudes not exceeding 240 metres above sea level. The density of large trees in this habitat exceeding 10 cm at breast height is estimated to range from 500 to 800 trees per hectare, and typical tree genera include Dipterocarpus and Ficus. The forest undergrowth predominantly comprises rattans, bamboos, shrubs and climbers. Because these habitats are largely inaccessible to humans, collecting data on this species is logistically difficult, which may partly explain why little is known about this stork's natural history.<p>Although Storm's stork accepts both lowland riverine forest and peat swamp forest, it is currently unknown which of these habitats provide optimal living conditions for the species. However, peat-swamp forest does appear to be an underestimated, ecologically important habitat for this stork across much of its range. In the wake of continued anthropogenic loss of lowland riverine forest, peat-swamp forest possibly provides an important refuge for the species and an extensive area of peat swamp forest occurs in West Kalimantan. However, this forest habitat is also under threat through conversion to palm oil plantations, logging and forest fires, so that increased conservation efforts should be directed on protecting peat-swamp forest.<p>This species has been shown to be somewhat tolerant of logged forests; however, these areas’ actual value as a breeding habitat for this species is disputed. Danielsen and Heegaard have considered Storm's stork incapable of breeding in logged forests despite apparent short term survival. In any case, current records have been too short to demonstrate long-term value of logged forests to this stork species. The acceptance of logged forests by Storm's stork may also entail some caveats; for example, that there must invariably be easy access within logged forest to freshwater margins, and that at least 20 years of forest regeneration should be allowed to elapse before real habitat value is re-established. A local mosaic of primary and logged forest may also explain this species’ apparent persistence in logged forest, because it may rely on the undisturbed forest patches as a refuge to sustain itself in the logged forest patches.<p>This stork is often seen soaring at great heights over rivers and forest clearings, and like many other storks utilises thermals to assist it in gliding. This behaviour is said to be "contagious" because when one individual begins to soar, conspecifics join it in flight; with flocks consisting of up to six individuals.On Borneo, it has also been reported on open, grassy freshwater swamps and paddy fields. It appears to never frequent saline habitats, but occasionally uses forested inland areas adjacent to bodies of water subject to tidal movements and near mangrove swamps.

Migration

Resident species

Behavior

Migration pattern: Resident species.

Conservation

Population trend: declining.

Population trend

declining