Justification of Red List Category
This species has an extremely large range, and hence does not approach the thresholds for Vulnerable under the range size criterion (Extent of Occurrence <20,000 km2 combined with a declining or fluctuating range size, habitat extent/quality, or population size and a small number of locations or severe fragmentation). Despite the fact that the population trend appears to be decreasing, the decline is not believed to be sufficiently rapid to approach the thresholds for Vulnerable under the population trend criterion (>30% decline over ten years or three generations). The population size is very large, and hence does not approach the thresholds for Vulnerable under the population size criterion (<10,000 mature individuals with a continuing decline estimated to be >10% in ten years or three generations, or with a specified population structure). For these reasons the species is evaluated as Least Concern.
The overall trend is decreasing, although some populations may be stable (Wetlands International 2006).
Behaviour This species makes irregular migratory, partially migratory or nomadic movements within Africa (del Hoyo et al. 1992, Hockey et al. 2005) to areas where changing water levels increase fish availability (Hockey et al. 2005). Some populations are also largely sedentary (del Hoyo et al. 1992). Breeding is seasonal and starts whenever food is most abundant according to local ecological conditions (e.g. when fish become concentrated in small wetlands or marshes [Hancock et al. 1992]), this may either be towards the end of the rains or during the dry season (del Hoyo et al. 1992). The species breeds colonially, often with other species (Brown et al. 1982, del Hoyo et al. 1992), usually in small groups of 10-20 pairs (Brown et al. 1982) (exceptionally as many as 50 pairs [Hancock et al. 1992]). It is a gregarious species but never aggregates into very large flocks (Brown et al. 1982), being more often observed in pairs or small flocks of up to 50 individuals (Hockey et al. 2005). At night it forms communal roosts in favoured roosting sites (e.g. sandbanks or trees), which may attract individuals from a wide area (Brown et al. 1982). Habitat The species inhabits a variety of wetlands (del Hoyo et al. 1992) with shallow water 10-40 cm deep for feeding (Hancock et al. 1992) and sandbanks or trees for roosting (del Hoyo et al. 1992). It frequents large swamps, the margins of rivers and lakes, lagoons (del Hoyo et al. 1992), large marshes, small pools (Hancock et al. 1992), flooded grassland (Hockey et al. 2005), alkaline lakes, reservoirs, waterholes and rice-paddies (del Hoyo et al. 1992), less commonly foraging on marine mudflats (del Hoyo et al. 1992), in tidal pools along beaches (Hancock et al. 1992) or in estuaries (Hockey et al. 2005). The species generally avoids areas of large-scale flooding and is rare in forested areas (although it may occur in wooded savanna [del Hoyo et al. 1992]). Diet Its diet consists of small aquatic prey such as frogs, small fish (del Hoyo et al. 1992), aquatic insects, worms, crustaceans and occasionally small mammals and birds (Hancock et al. 1992). Breeding site The nest is constructed of sticks (del Hoyo et al. 1992) and is positioned in small trees over water or high up in larger trees on dry land (Hancock et al. 1992) (e.g. Accacia spp., Bombax spp. [del Hoyo et al. 1992] or baobabs [Brown et al. 1982]). The species nests colonially in single- or mixed-species groups (del Hoyo et al. 1992) with up to 10-20 pairs per tree (Brown et al. 1982) (occasionally up to 50 pairs [Hancock et al. 1992]), neighbouring nests usually spaced 1-3 m apart (Hockey et al. 2005).
Text account compilers
Ekstrom, J., Butchart, S., Malpas, L.
BirdLife International (2023) Species factsheet: Mycteria ibis. Downloaded from http://datazone.birdlife.org/species/factsheet/yellow-billed-stork-mycteria-ibis on 10/06/2023. Recommended citation for factsheets for more than one species: BirdLife International (2023) IUCN Red List for birds. Downloaded from http://datazone.birdlife.org on 10/06/2023.