Storm's stork (Ciconia stormi) is a medium-sized stork species that occurs primarily in lowland tropical forests of Malaysia, Indonesia and southern Thailand. It is considered to be the rarest of all storks,Hancock JA, Kuschlan JA, Kahl, MP. 1992. Storks, Ibises and Spoonbills of the World. Academic Press. and is estimated to number at most 1,750 wild individuals across its geographic range. The population has long been in decline and the primary cause is widely considered to be deforestation of its native habitat.
Taxonomy and systematics
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.Boelens B, Watkins M, Grayson M. 2014. The Eponym Dictionary of Birds. Bloomsbury, UK. 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.
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,Chasen FN. 1935. Hand List of Malaysian Birds. Bulletin of Raffles Museum 11. 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.
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.
Description 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.oiseauxbirds.com. http://www.oiseaux-birds.com/card-storm-s-stork.html.Accessed 03/06/16
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.
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.
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.
The adult birds are generally silent outside the breeding season; however, during the breeding season they utter vocalisations that have been transcribed as "Kurau".Smythies BE. 1981. The Birds of Borneo, 3rd Edition. Malayan Nature Society, Kuala Lumpur. 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.
Distribution 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.
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 thereRound P. 1988. Threatened forest birds of Thailand. ICBP Technical Publication Number 8. Cambridge: International Council for Bird Preservation. and since then was previously considered extinct in Thailand.BirdLife International. 2001. Threatened birds of Asia: The Birdlife International Red Data Book. Cambridge, U.K.: BirdLife International. 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.
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.
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.
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 HeegaardDanielsen F, Heegaard M. 1995. Impact of logging and plantation development on species diversity: a case study from Sumatra. In: Sandbukt Ø. 1995. Management of tropical forests: towards an integrated perspective. Oslo: Centre for Development and the Environment, University of Oslo. 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.Berdie IJ, 2008. Assessing canopy cover requirements of Storm's Stork Ciconia stormi at multiple scales. Open access thesis. Paper 132. 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.
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,Meijaard E, Dennis R, Schroor P, Nardiyono, Berdie I, Douglas O, Fuller. 2015. Habitat characteristics of Storm's stork Ciconiia stormi in Indonesian Borneo. Available at: https://www.researchgate.net/publication/272182067_Habitat_characteristics_of_Storm's_Stork_Ciconia_stormii_in_Indonesian_Borneo. Accessed 30/05/16. but occasionally uses forested inland areas adjacent to bodies of water subject to tidal movements and near mangrove swamps.
Behaviour and ecology
Breeding Two major breeding records of this species have been made; in southern Thailand in 1986, and in swamp forest in southern Sumatra in 1989. However, chicks in the Thailand breeding record were first observed in October and those in Sumatra were first observed in early June. The differing recorded times of egg laying in this species therefore does not suggest a strict breeding season. Collective breeding records of this species are currently scant possibly because nests are difficult to accurately locate in the dense forest habitat.
The nest is usually located 19-30m above ground above riverbanks, often in the forks of trees of Dipterocarpus species. At south Sumatra, a Storm's stork nest was studied that lay 8.3m above ground in an 18m-tall Rhizosphora mucronata tree. In captivity, both the male and female have been observed to carry out nest-building activities. The nest has an external outer diameter measuring between 30 and 50 cm; with a depth of 10–15 cm, and is typically composed of twigs and sticks mainly belonging to tree species in the genus Rhizosphora, but also from species in the families Loranthaceae, Dipterocarpaceae, and Rubinaceae. These sticks measure 15– 60 cm in length and 0.5-1.5 cm in diameter. The nest interior is lined with soft material such as grass and down. 2–4 cm long leaflets from Xylocarpus species have also been identified as nest material, and these plants have been found growing in the area surrounding the nest. The same nest is often used by a pair over consecutive years; whereby both mates add more material to the nest each year.