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). The population trend is not known, but the population is not believed to be decreasing sufficiently rapidly to approach the thresholds 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 global population is estimated to number c.790,000-3,700,000 individuals (Wetlands International 2015). This roughly equates to 500,000-2,500,000 mature individuals. The European population is estimated at 223,000-391,000 pairs, which equates to 447,000-782,000 mature individuals (BirdLife International 2015). National population estimates include 100,000-1 million breeding pairs and > 10,000 individuals on migration in China; 100-10,000 breeding pairs and 1,000-10,000 wintering individuals in Korea; 100,000-1 million breeding pairs and > 10,000 wintering individuals in Japan; and 100,000-1 million breeding pairs and > 10,000 individuals on migration in Russia (Brazil 2009).
The overall population trend is uncertain, as some populations are decreasing, while others are stable, increasing or have unknown trends (Wetlands International 2015). A moderate increase between 1980 and 2013 has been estimated for the European population (EBCC 2015). However the European breeding population is thought to have undergone a short-term decline between 2000 and 2012 (BirdLife International 2015).
Behaviour Most Palearctic populations of this species are fully migratory, dispersing widely in September-October after the breeding season and returning to breeding grounds in February (Kushlan and Hancock 2005). Further south, populations tend to be sedentary or only partially migratory. Most migratory movements occur nocturnally, with birds moving in small parties or larger flocks of 200-250 (Brown et al. 1982). The species breeds January-May in the Palearctic Region, and in spring and summer in temperate areas, but mainly during the rains in Africa and the tropics (although here it may also breed in any month of the year) (Kushlan and Hancock 2005). It breeds in mixed colonies of hundreds or thousands of pairs (the largest colony in Europe is 800-1,300 pairs), although it may also nest solitarily or in small groups of 2-10 nests (Kushlan and Hancock 2005). The species is typically a solitary feeder but at abundant temporary food sources, or where available feeding areas are restricted, large congregations may occur (Snow and Perrins 1998, Kushlan and Hancock 2005). It feeds at any time day or night, but is most active at dawn or dusk, typically roosting communally or solitary during the middle of the day and at night in trees and on cliffs, low rocks, islets or along shores (Brown et al. 1982, Kushlan and Hancock 2005).
Habitat This species is a generalist in its habitat use, although shallow water, relatively large prey, and four or five months of ice-free breeding season are among the essential characteristics of its habitat (Kushlan and Hancock 2005). It occurs from sea-level up to 500 or even 1,000 m, occasionally breeding much higher (Snow and Perrins 1998) (2,000 m in Armenia, 3,500-4,000 m in Ladakh, north-west India), inhabits any kind of shallow water, either fresh, brackish or saline, both standing or flowing, and shows a preference for areas with trees as it is commonly an arboreal rooster and nester. Some degree of isolation and protection are also typical of places chosen for roosting and nesting (Kushlan and Hancock 2005). The species is found inland on broad rivers, narrow streams, lake shores, ornamental ponds, fish-ponds, marshes, flood-plains, reeds swamps, rice-fields and other irrigated areas, river oxbows, reservoirs, ditches, canals, sewage farms, inland deltas, and on islets and emerging rocks (Brown et al. 1982, Snow and Perrins 1998, Kushlan and Hancock 2005). On the coast the species also frequents deltas, salt-marshes, mangroves, estuaries, tidal mudflats, muddy and sandy shores, and sand-spits (Brown et al. 1982, Snow and Perrins 1998, Kushlan and Hancock 2005).
Diet Its diet consists predominantly of fish and eels 10-25 cm long, as well as amphibians, crabs, molluscs, crustaceans, aquatic insects, snakes, small rodents, small birds and plant matter (although this may be incidental, or only to aid in pellet formation) (Brown et al. 1982, Snow and Perrins 1998, Kushlan and Hancock 2005).
Breeding site The nest is a stick platform that is often re-used over successive years, usually positioned high in a tall tree up to 50 m, but also on the ground or on cliff edges, in reedbeds or in bushes. In reed-beds nests may be built of reeds, and ground nests may be reduced to a slight scrape, ringed with small stones and debris (Snow and Perrins 1998, Kushlan and Hancock 2005). The species commonly nests in colonies, and nesting sites are typically situated 2-38 km (convenient flying distance) from preferred feeding areas (Kushlan and Hancock 2005).
In Europe, the species was heavily persecuted in the nineteenth century due to its consumption of fish, which resulted in competition with fishermen and fish farmers (Kushlan and Hancock 2005). Although killing at aquaculture farms has not reduced the global population so far (possibly because it is young birds that are mostly killed), 800 individuals are estimated to have died per year at Scottish fish-farms between 1984 and 1987 by being shot, drowned or poisoned by fish farmers (Carss 1994, Kushlan and Hancock 2005). Renewed hunting poses a threat to populations in Bavaria (Germany) by decreasing numbers to levels that inhibit recovery following severe winters (severe winters increase mortality rates for juveniles) (Kushlan and Hancock 2005). The species is vulnerable in Madagascar owing to its restricted range, exceedingly high levels of habitat alteration (from siltation and the need for agricultural land for rice and grazing), hunting, and predation at nesting colonies (Kushlan and Hafner 2000, Kushlan and Hancock 2005). Timber harvesting is a threat throughout much of the species's range by removing trees used by nesting colonies and/or disturbing nearby colonies (Kushlan and Hancock 2005). The species is also susceptible to avian influenza (Melville and Shortridge 2006) and avian botulism (van Heerden 1974), so may be threatened by future outbreaks of these diseases.
Utilisation The species is hunted and traded at traditional medicine markets in Nigeria (Nikolaus 2001).
Conservation Actions Underway
The species is not listed on priority lists of the Conventions.
Conservation Actions Proposed
The following information refers to the species's European range only: Freshwater habitats need to be sustainably managed. Establish non-intrusion zones and stop logging around colonies.
Text account compilers
Malpas, L., Ekstrom, J., Ashpole, J, Butchart, S., Everest, J.
BirdLife International (2021) Species factsheet: Ardea cinerea. Downloaded from http://www.birdlife.org on 21/09/2021. Recommended citation for factsheets for more than one species: BirdLife International (2021) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 21/09/2021.