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• Text account
• Data table and detailed info
• Distribution map
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Justification of Red List category
Ciconia stormi is native to the swamp and plains-level forests of the Greater Sundas, where it occurs at a very low density and nowhere is numerous. Over the past three generations (31 years: 1992–2023), it is suspected of having declined rapidly (40–60%) in response to industrial removal of its habitat for agro-industry plantations, particularly oil-palm and rubber. Its global population size is uncertain, but probably numbers 300–1,750 mature individuals; with ongoing habitat loss compounded by forest fires which may increase with frequency in response to climate change, this species is considered to be a high risk of extinction in the near-term. Accordingly, it is listed as Endangered.

Population justification
The population size of this species has not recently been formally estimated. In Thailand, any population that persists must be wholly relictual, and potential future records are likely to stem from neighbouring Myanmar, where there are sightings from Lenya National Park (eBird 2023). In Myanmar itself, there is little habitat away from Lenya, where sightings are sporadic and rare, suggesting only a tiny (<10 pairs) population persists. In Peninsular Malaysia, there are no records away from Taman Negara in the past decade, and here too the population is assumed to be tiny (again, set arbitrarily to <10 pairs). On Sumatra, too, the population is assumed to be relatively small, with recent records from only Siberut Island, Way Kambas National Park, the Kampar Peninsula (RER 2017, eBird 2023). Danielsen et al. (1997) estimated that there were fewer than 100 mature individuals left on Sumatra and there is little doubt the population will have reduced since then following the contraction of lowland peatswamp forest. Accordingly, and incorporating the number and spread of eBird (2023) records, the Sumatran population (including Siberut) is estimated at 50–100 mature individuals.
Modern records in Sabah are concentrated along the Kinabatangan River (in large part a reflection of observer effort). However there are also records from other large areas of lowland forest, including Tabin Wildlife Reserve, Deramakot Forest Reserve and Danum Conservation Area. The number of individuals at these sites is ultimately unknown, although observers rarely record more than 1-2 individuals at one time (eBird 2023). Records from Brunei and Sarawak are sporadic and typically refer to single birds flying over (eBird 2023); it is therefore unclear whether these refer to breeding individuals, or wanderers from elsewhere on Borneo. Certainly, the area of suitable habitat for the species here is now small and greatly reduced, as is reflected by the scarcity of other large-bodied peatswamp forest specialists in these areas (e.g. Lophura pyronota, Rhyticeros undulatus), despite them being collected there historically (BirdLife International 2001, Mann 2008). Within Borneo itself, there can be little doubt that Kalimantan now hosts (perhaps considerably) more birds than anywhere else, with particular strongholds in the peatswamp forests of Central Kalimantan and East Kalimantan provinces. Nonetheless, even here data suggest that it occurs at a very low density and/or ranges widely (see summary of recent records in Kalimantan presented in Martin et al. 2022). Across Borneo, Singh et al. (2021) estimated that the area of suitable habitat for Storm's Stork was (in 2010) only 3,950 km². Applying a density of just 20-40 mature individuals within 1,100 km² of primary forest on Sumatra (per Danielsen et al. 1997) suggests a Bornean population size of 80-160 mature individuals, however there are several reasons this is improbably low. Foremost, in several areas of Kalimantan, data suggest that this species can occur at a considerably higher density where habitat is optimal: for example, Purbowo et al. (2017) found nine birds in a very small (<1 km²) area of swamp forest along the Kepuluk river. Moreover, such a low density is difficult to rationalise with the frequency and spread of recent records (e.g. eBird 2023), even accepting that this species is mobile and most frequently observed when soaring. For these reasons, across the optimal habitat identified by Singh et al. (2021), densities are suspected of being 3–10x higher than those suggested by Danielsen et al. (1997), which produces an overall density far more consistent with the numbers and frequency of Storm's Storks observed by citizen scientists (eBird 2023) and reported in the literature (e.g., Martin et al. 2022). Therefore, the population on Borneo is estimated number 240–1,600 mature individuals.
Data across this species' global range suggest that previous estimations of a global population <350 mature individuals (M. Silvius in litt. 2002, Y. Noor Rusila in litt. 2002) was possibly pessimistic, notwithstanding the rapid rate of reduction the population size has probably experienced over the past 50 years. Nonetheless, the lower bounds of each area calculated here sum to only c. 300 mature individuals, suggesting that this is a plausible scenario. However, a much larger upper bound (c. 1,750) is used here, accounting for the great uncertainty over the total population on Borneo (in particular Kalimantan).

Trend justification
Although there are no direct population data for this species from which to accurately derive trends, comparing the spread of historic records (e.g. BirdLife International 2001, Mann 2008), with more recent data (eBird 2023), indicates that there is no doubt Ciconia stormi has greatly contracted its range over the past three generations, with it no longer being found at many sites it once occupied. The landscape-scale removal of swamp and plains-level forests for plantations (principally oil palm, but also rubber) has been the principal driver of this (Miettinen et al. 2011), and while rates of forest loss have recently slowed (especially in Kalimantan: Global Forest Watch 2023), the practice still continues and there is no reason to suspect that this species has ceased declining. Moreover, some populations (especially those in Peninsular Malaysia and, perhaps, on Sumatra) are now so small and isolated, with very little breeding habitat, that they may not be viable population units in the future. Accordingly, the species is inferred to be undergoing a continuing decline.
The rate of decline over the past three generations is more difficult to determine, in part owing to knowledge gaps in this species' habitat tolerances. Although it has frequently been observed in degraded forest (e.g., Martin et al. 2022, and sources listed therein), Berdie (2008) determined that the species is nonetheless dependent on (nearby) closed canopy forest, and the only breeding records have been from lowland primary forest (Danielsen et al. 1997, Posa and Marques 2012). In the absence of other data from which to generate more robust trends, remote sensing data and the extent of suitable habitat are used as a proxy for population size. Between 2000 and 2023, the extent of forest cover within this species' elevational range reduced by 34–39%, depending on the assumptions used (Global Forest Watch 2023, based on data from Hansen et al. [2013] and methods disclosed therein). This is equivalent to a rate of c.44–53% over three generations. To account for additional uncertainty (for example, whether fragmentation or degradation has had any impact), over the past three generations (31 years: 1992–2023) the rate of decline is placed in a broader bracket of 40–60%. Given this species is long-lived, slow to breed, and unlikely to recover quickly, the population is also suspected of having declined by 40–60% between 1995 and 2026 (thus meeting the thresholds for Endangered under Criteria A2 and A4). Rates of future decline are far more difficult to predict. Only 11.5% of suitable habitat identified by Singh et al. (2021) is protected, however the same authors also determined that habitat loss between 2010 and 2050 would be only 16.6–19.2% under a range of land-use and climate change scenarios. In the period 2020–2022, the rate of forest cover loss in this species' range also fell (to an equivalent rate of 15–22% over three generations: Global Forest Watch 2023), in large part due to a slow down in forest loss in Kalimantan. Given the long generation length and resulting large window, accurately predicting population declines over the next three generations (31 years: 2023–2054) is very challenging, but is here suspected to lie somewhere in the bracket 10–40%, incorporating the fact that future declines are likely, but at a rate probably slower than those observed in the past.

Historically this species was widespread through the Greater Sundas, where it occurred from the southernmost end of Peninsular Thailand and Myanmar, south through Peninsular Malaysia, and on Sumatra, Indonesia, and Borneo, where it is recorded from all states, including Brunei. It is now effectively extinct in Thailand, although sightings in neighbouring Lenya National Park, Myanmar, suggest birds may have the propensity to wander into Thai territory (e.g. Cutter et al. 2007). There are recent records from all other parts of the range, although the species occurs at a very low density and is nowhere numerous.

It occurs at low densities in large, undisturbed blocks of level lowland forest, particularly freshwater and peat-swamp forests, on the floodplains of large rivers. It also frequents disturbed, recently burned and logged areas, and occasionally areas subject to tidal movements, although these may constitute suboptimal habitats and breeding records are confined to primary forest (Danielsen et al. 1997, Cheyne et al. 2014). It is generally solitary, but is occasionally found in small groups. Two eggs are usually laid and the chicks are able to fly after c. 90 days.

This species is suspected to have declined by 40-60% over the past three generations (31 years: 1992-2023). The main, if not entire, cause of such rapid declines is the widespread and large-scale clearance of the lowland forests upon which this depends (Berdie 2008) to make space for plantations, chiefly oil-palm and, to a lesser extent, rubber and timber. These losses have disproportionately impacted peatswamp forests (Miettinen et al. 2011), which host the largest populations of this species. While this species has been observed in degraded habitats, there is no evidence they can persist in plantations, and breeding has been observed only in primary forest (see Discussion in Martin et al. [2022]). Forest fires are also a risk, especially in dry El Niño years (Harrison et al. 2016). There is little evidence this species is hunted; incidental (mostly subsistence) hunting almost certainly occurs, but there is no evidence this is a factor in its decline.

Conservation Actions Underway
Legally protected in Thailand, Malaysia and Indonesia. This species occurs in numerous protected areas (UNEP-WCMC and IUCN 2023), which combined protect over 11% of suitable habitat (see Singh et al. 2021).

Conservation Actions Proposed
Continue further surveys to determine its distribution, population and habitat requirements, particularly in Kalimantan (e.g. Cheyne et al. 2014). Establish further protected areas at sites supporting significant populations, including gazetting proposed reserves, particularly on Sumatra and in Kalimantan. Lobby for the cessation of logging in swamp-forests. Improve effectiveness of protection measures in protected areas in Indonesia.

75-91 cm. Secretive, black-and-white stork with red bill, orange facial skin and golden-yellow area around eye. Black lower foreneck. Juvenile has dark plumage parts somewhat browner than adult, dark-tipped bill and duller bare parts. Similar spp. Woolly-necked Stork C. episcopus has white lower foreneck, dark bill and bronze coloration on inner wing-coverts.

Text account compilers
Berryman, A.

Contributors
Davidson, G., Hearn, A., Martin, R., Noor Rusila, Y., Silvius, M. & van Balen, B.S.

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Recommended citation
BirdLife International (2024) Species factsheet: Storm's Stork Ciconia stormi. Downloaded from https://datazone.birdlife.org/species/factsheet/storms-stork-ciconia-stormi on 23/12/2024.
Recommended citation for factsheets for more than one species: BirdLife International (2024) IUCN Red List for birds. Downloaded from https://datazone.birdlife.org/species/search on 23/12/2024.