Rationale
(Changed due to Criteria revision)
Although the Yellow-billed Stork Mycteria ibis is a reasonably common sight at wetlands in much of the region, the species currently breeds at only a single site. As such it was assessed as Critically Endangered based on its restricted (breeding) AoO plus extreme fluctuations in numbers of mature individuals. However, it is likely that the regional population receives an immigration of individuals capable of reproducing in the region, and that there is a high likelihood of this immigration continuing; consequently the species was downlisted from regionally Critically Endangered to regionally Endangered.
Distribution
The Yellow-billed Stork occurs throughout sub-Saharan Africa and western Madagascar (del Hoyo et al. 1992). It is widespread within the region, but avoids arid western areas and has been described as a faculatively nomadic species (del Hoyo et al. 1992). Some individuals are always present and presumably resident, but the regional population is supplemented by migrants from the north (Anderson 1997), especially during summer; some immigrants, most of which are probably from the southern Africa, may breed in South Africa. Breeding occurs regularly only at Nsumo Pan in Mkuze Game Reserve (IBA SA057) in KwaZulu-Natal (Bowker and Downs 2012), with historical records from Pongola Nature Reserve in 1985-1986 (Tarboton et al. 1987). There are isolated breeding records from Engelhardt Dam, Kruger National Park (Newman 1980) and Nylsvley (Tarboton 1995). The AoO of a mere 2 km2 is based upon the extent of the breeding range, i.e. Nsumo Pan.
Population
The global population has been estimated at 75 000-100 000 mature individuals (Dodman and Diagana 2006). Johnson (2000) estimated a minimum of 300 individuals for the region, with 200 in KwaZulu-Natal, although Anderson (2005) believed this to be an underestimate. Bowker and Downs (2012) provided data for breeding pairs at Nsumo Pan from 1986-2010 which show large fluctuations in numbers. A minimum of five pairs was recorded in 1989 and a maximum of 163 pairs (370 adults) was observed in 2009. Sixty-four pairs (124 adults) were recorded in 2010. The regional population is estimated to be between 150-350 mature individuals although is subject to large fluctuations. Confidence in this regional population estimate is medium.
Population trend
The global population is decreasing, although some populations are stable (Dodman and Diagana 2006). The highly mobile nature and seasonal occurrence make it difficult to detect any population trends and may mask possible declines (Johnson 2000). Based on the Nsumo Pan data (Bowker and Downs 2012), the regional population has increased over the past three generations (25 years). This increase may be partially explained by the loss of the Pongola colony in the early 1980s (Tarboton et al. 1987). In addition, a marked fluctuation in the number of pairs breeding at Nsumo Pan may indicate that there are annual movements of birds from Nsumo Pan to and from sites in neighbouring countries. Alternatively, environmental conditions may limit breeding events. Despite the large fluctuations, the regional population is stable to slightly increasing over a three generation period. Confidence in this trend estimate is medium.
Threats
The main threat to the Yellow-billed Stork is loss of wetland habitats, including the system of pans, marshes and floodplains on which the birds depend for foraging (Monadjem et al. 2003, Anderson 2005). Loss of suitable trees for the birds to nest in at Pongolapoort Dam resulted in the loss of a breeding colony of around 20 nests in the 1980s (Tarboton et al. 1987).
Conservation
Underway
There are no species-specific conservation measures underway. Nsumo Pan is situated within the Mkuze section of the iSimangaliso Wetland Park. The Park is listed as a provincial nature reserve as well as an UNESCO World Heritage Site. Globally, the Yellow-billed Stork is listed on Appendix II of the Bonn Convention. Regionally, it is listed as Near Threatened in Swaziland and is protected under the Swaziland Game Act (1991).
Proposed
Nesting sites for large, water-associated, colonially nesting birds are crucial for recruitment and maintenance of the population status and conservation of such species; maintenance of the Nsumo Pan site is essential to retain the Yellow-billed Stork as a regionally breeding species. Monitoring of the Nsumo Pan colony, in partnership with relevant stakeholders, needs to be sustained. Re-assessment of historic breeding sites may suggest possibilities for rehabilitation and re-occupation particularly through the establishment of artificial nesting sites at suitable locations.
Research
* Effects of environmental conditions on dynamics of the Nsumo Pan colony need to be investigated.
* Suspected movements of individuals between Nsumo Pan and neighbouring countries need to be confirmed.
* Incidental breeding or irruptive occurrences need to be documented to clarify regional movements.
