Justification 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.

Family/Sub-family Ardeidae

Species name author (Linnaeus, 1758)

Taxonomic source(s) AERC TAC (2003), AOU checklist (1998 + supplements), Christidis and Boles (1994), Cramp and Simmons (1977-1994), Dowsett and Forbes-Watson (1993), SACC (2005 + updates), Sibley and Monroe (1990, 1993), Stotz et al. (1996), Turbott (1990)

Synonyms Ardea alba SACC (2005), Ardea alba AOU checklist (1998 + supplements), Egretta alba Turbott (1990), Egretta alba Stotz et al. (1996), Egretta alba Dowsett and Forbes-Watson (1993), Egretta alba Cramp and Simmons (1977-1994)

Population estimate

Population trend

Range estimate (breeding/resident)

Country endemic?

590,000 - 2,200,000

unset

74,700,000 km²

No

Important Bird Areas Click here to view map showing IBAs where species is recorded and triggers any of the IBA criteria.

Ecology: Behaviour All populations of this species undergo post-breeding dispersive movements¹. Populations breeding in the tropics are sedentary¹ or partially migratory (in relation to rainfall)⁴, whereas Palearctic and Nearctic populations are migratory^{1, 6}. The timing of the breeding season varies geographically¹ although temperate breeders tend to nest in the spring and summer (e.g. April to July) and tropical breeders nest in the part of the rain cycle when food becomes maximally available (this may be during the rains or in the dry season)². The species typically breeds in colonies of tens, hundreds or even a thousand pairs^{1, 2}, sometimes with other species (e.g. 450 pairs in a mixed colony of over 3,000 nests in Australia)¹. Some populations also show a tendency to breed solitarily or in small groups¹. Outside of the breeding season the species may feed solitarily¹ or in small loose groups⁹ (e.g. of 12-50 individuals)⁴, although flocks of hundreds or more individuals may form where food is abundant¹. The species is a diurnal feeder¹ but is most active at dawn and dusk (although in coastal environments it feeding habits are determined by tidal stages)², and roosts at night in trees⁴ alongside lakes or rivers or in mangroves, often with other species⁷. Habitat The species inhabits all kinds of inland and coastal wetlands¹ although it is mainly found along the coast in the winter (e.g. in the Palearctic Region)⁸ or during droughts (e.g. in Australia)⁹. It frequents river margins, lakes shores, marshes, flood-plains¹, oxbows, streams⁸, damp meadows², rice-fields, drainage ditches¹, aquaculture ponds, reservoirs^{2, 9} and sewage works^{5, 9} inland, and the shallows of salt-lakes⁹, saltpans, mudflats, coastal swamps, mangroves¹, saltmarshes, seagrass flats, offshore coral reefs, lagoons² and estuaries when in coastal locations¹. Diet In aquatic habitats its diet consists of fish, amphibians, snakes, aquatic insects and crustaceans although in drier habitats terrestrial insects, lizards, small birds and mammals are more commonly taken¹. Breeding site The nest is constructed from sticks² and vegetation⁴ and is normally positioned over water at a height of 1-15 m² in reedbeds, bamboos², bushes, trees¹ (e.g. willow Salix spp.), mangroves³ and other plants near water or on islands in sites that are protected from ground predators². The species usually nests colonially in single- or mixed-species groups where nests may be less than 1 m apart or touching, although they are usually placed more spread out in reedbeds². Breeding pairs may also reuse nests from previous years². Management information Breeding site conservation should include colony protection, control of disturbance and vegetation management, and the conservation of feeding areas should include the management of hydrology, salt intrusion, contaminants and disturbance². An artificial island nesting site created in the Camargue, France succeeded in attracting nesting pairs to the area¹⁰.

Threats The species is threatened by wetland habitat degradation and loss^{1, 9} for example through drainage, grazing, clearing, burning, increased salinity, groundwater extraction and invasion by exotic plants⁹. Breeding colonies in Madagascar may be declining due to egg and chick gathering from colonies by local peoples^{2, 7} and the species previously suffered from intense persecution for the plume trade (this is no longer a threat)¹.

References 1. del Hoyo et al. (1992). 2. Kushlan and Hancock (2005). 3. Hancock and Kushlan (1984). 4. Brown et al. (1982). 5. Hockey et al. (2005). 6. Flint et al. (1984). 7. Langrand (1990). 8. Snow and Perrins (1998). 9. Marchant and Higgins (1990). 10. Hafner (2000).

Further web sources of information

Detailed species account from Birds in Europe: population estimates, trends and conservation status (BirdLife International 2004)

Text account compilers Stuart Butchart (BirdLife International), Jonathan Ekstrom (BirdLife International), Patricia Escalante (CIPAMEX - Instituto de Biología), Lucy Malpas (BirdLife International)

IUCN Red List evaluators Jeremy Bird (BirdLife International), Stuart Butchart (BirdLife International)

Recommended citation BirdLife International (2009) Species factsheet: Casmerodius albus. Downloaded from http://www.birdlife.org on 10/2/2010

This information is based upon, and updates, the information published in BirdLife International (2000) Threatened birds of the world. Barcelona and Cambridge, UK: Lynx Edicions and BirdLife International, BirdLife International (2004) Threatened birds of the world 2004 CD-ROM and BirdLife International (2008) Threatened birds of the world 2008 CD-ROM. These sources provide the information for species accounts for the birds on the IUCN Red List.

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