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 population is estimated to number 300,000-500,000 individuals in total.
The population is considered to be stable (Wetlands International 2018).
Behaviour This species is an intra-African trans-equatorial migrant, making movements that are triggered by the rains (del Hoyo et al. 1992, Hancock et al. 1992). It breeds during in the rains when snails (its main prey items) are most readily available. It nests in colonies of various sizes, often with other species (del Hoyo et al. 1992, Hancock et al. 1992). Nesting may only occur in years when local food supplies are plentiful; however, it may not occur regularly at the same site (Hancock et al. 1992). The species feeds in loose groups that may contain up to 50 well-dispersed individuals; flocks of over 7,000 may also occur in some seasons (Brown et al. 1982, Hancock et al. 1992). It migrates in flocks and roosts communally in trees (Brown et al. 1982, del Hoyo et al. 1992).
Habitat The species inhabits freshwater wetlands with shallow waters and a large abundance of aquatic molluscs, including marshes, swamps, rice-fields, flood-plains, the backwaters and margins of lakes or rivers, ponds and streams (del Hoyo et al. 1992, Hancock et al. 1992). It may also frequent moist savanna or burnt grassland, as well as occasionally forest clearings, coastal mudflats and mangrove swamps (del Hoyo et al. 1992, Hancock et al. 1992).
Diet In many regions, the species may depend entirely upon molluscs such as aquatic snails (e.g. Pila spp. or Lanistes ovum) and freshwater mussels (Ampullaria spp.) (del Hoyo et al. 1992, Hancock et al. 1992). Other prey items taken include frogs, crabs, worms, fish and insects (e.g. locusts and beetles) (del Hoyo et al. 1992, Hancock et al. 1992).
Breeding site The nest is a small platform of sticks and vegetation positioned in trees and bushes over water (e.g. inundated in standing water on flood-plains), or alternatively in reedbeds (Brown et al. 1982, del Hoyo et al. 1992, Hancock et al. 1992). It nests colonially, often in mixed-species groups (Hancock et al. 1992).
The species is threatened by habitat loss, entanglement in fishing lines and environmental pollution (e.g. pesticides applied to water for mosquito control) (Hockey et al. 2005). It also suffers from hunting, poaching and the destruction of breeding colonies by villagers on Madagascar (del Hoyo et al. 1992, Hancock et al. 1992).
Utilisation The species is hunted and traded at traditional medicine markets in Nigeria (Nikolaus 2001).
Text account compilers
Butchart, S., Malpas, L., Ekstrom, J.
BirdLife International (2020) Species factsheet: Anastomus lamelligerus. Downloaded from http://www.birdlife.org on 28/10/2020. Recommended citation for factsheets for more than one species: BirdLife International (2020) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 28/10/2020.