Species

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.

Taxonomic source(s)
AERC TAC. 2003. AERC TAC Checklist of bird taxa occurring in Western Palearctic region, 15th Draft. Available at: http://www.aerc.eu/DOCS/Bird_taxa_of _the_WP15.xls.
AOU. 1998. Check-list of North American birds. American Ornithologists' Union, Washington, D.C.
Christidis, L.; Boles, W. E. 1994. The taxonomy and species of birds of Australia and its territories. Royal Australasian Ornithologists' Union, Melbourne.
Cramp, S.; Perrins, C. M. 1977-1994. Handbook of the birds of Europe, the Middle East and Africa. The birds of the western Palearctic. Oxford University Press, Oxford.
Dowsett, R. J.; Forbes-Watson, A. D. 1993. Checklist of birds of the Afrotropical and Malagasy regions. Tauraco Press, Li
SACC. 2006. A classification of the bird species of South America. Available at: http://www.museum.lsu.edu/~Remsen/SACCBaseline.html.
Sibley, C. G.; Monroe, B. L. 1990. Distribution and taxonomy of birds of the world. Yale University Press, New Haven, USA.
Stotz, D. F.; Fitzpatrick, J. W.; Parker, T. A.; Moskovits, D. K. 1996. Neotropical birds: ecology and conservation. University of Chicago Press, Chicago.
Turbott, E. G. 1990. Checklist of the birds of New Zealand. Ornithological Society of New Zealand, Wellington.

Taxonomic note
Casmerodius albus (Sibley and Monroe 1990, 1993) is retained as a cross-regional species contra Christidis and Boles (2008) who move C. albus into the genus Ardea and split it into two cross-regional species A. alba and A. modesta (note gender agreement of specific name for alba).

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

Population justification
Estimate includes totals for 'Ardea modesta'.

Trend justification
The overall population trend is uncertain, as some populations are decreasing, while others are increasing, stable fluctuating or have unknown trends (Wetlands International 2006). This species has undergone a large and statistically significant increase over the last 40 years in North America (177% increase over 40 years, equating to a 29% increase per decade; data from Breeding Bird Survey and/or Christmas Bird Count: Butcher and Niven 2007) Note, however, that these surveys cover less than 50% of the species's range in North America.

Ecology
Behaviour All populations of this species undergo post-breeding dispersive movements (del Hoyo et al. 1992). Populations breeding in the tropics are sedentary (del Hoyo et al. 1992) or partially migratory (in relation to rainfall) (Brown et al. 1982), whereas Palearctic and Nearctic populations are migratory (Flint et al. 1984, del Hoyo et al. 1992). The timing of the breeding season varies geographically (del Hoyo et al. 1992) 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) (Kushlan and Hancock 2005). The species typically breeds in colonies of tens, hundreds or even a thousand pairs (del Hoyo et al. 1992, Kushlan and Hancock 2005), sometimes with other species (e.g. 450 pairs in a mixed colony of over 3,000 nests in Australia) (del Hoyo et al. 1992). Some populations also show a tendency to breed solitarily or in small groups (del Hoyo et al. 1992). Outside of the breeding season the species may feed solitarily (del Hoyo et al. 1992) or in small loose groups (Marchant and Higgins 1990) (e.g. of 12-50 individuals) (Brown et al. 1982), although flocks of hundreds or more individuals may form where food is abundant (del Hoyo et al. 1992). The species is a diurnal feeder (del Hoyo et al. 1992) but is most active at dawn and dusk (although in coastal environments it feeding habits are determined by tidal stages) (Kushlan and Hancock 2005), and roosts at night in trees (Brown et al. 1982) alongside lakes or rivers or in mangroves, often with other species (Langrand 1990). Habitat The species inhabits all kinds of inland and coastal wetlands (del Hoyo et al. 1992) although it is mainly found along the coast in the winter (e.g. in the Palearctic Region) (Snow and Perrins 1998) or during droughts (e.g. in Australia) (Marchant and Higgins 1990). It frequents river margins, lakes shores, marshes, flood-plains (del Hoyo et al. 1992), oxbows, streams (Snow and Perrins 1998), damp meadows (Kushlan and Hancock 2005), rice-fields, drainage ditches (del Hoyo et al. 1992), aquaculture ponds, reservoirs (Marchant and Higgins 1990, Kushlan and Hancock 2005) and sewage works (Marchant and Higgins 1990, Hockey et al. 2005) inland, and the shallows of salt-lakes (Marchant and Higgins 1990), saltpans, mudflats, coastal swamps, mangroves (del Hoyo et al. 1992), saltmarshes, seagrass flats, offshore coral reefs, lagoons (Kushlan and Hancock 2005) and estuaries when in coastal locations (del Hoyo et al. 1992). 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 taken (del Hoyo et al. 1992). Breeding site The nest is constructed from sticks (Kushlan and Hancock 2005) and vegetation (Brown et al. 1982) and is normally positioned over water at a height of 1-15 m (Kushlan and Hancock 2005) in reedbeds, bamboos (Kushlan and Hancock 2005), bushes, trees (del Hoyo et al. 1992) (e.g. willow Salix spp.), mangroves (Hancock and Kushlan 1984) and other plants near water or on islands in sites that are protected from ground predators (Kushlan and Hancock 2005). 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 reedbeds (Kushlan and Hancock 2005). Breeding pairs may also reuse nests from previous years (Kushlan and Hancock 2005). 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 disturbance (Kushlan and Hancock 2005). An artificial island nesting site created in the Camargue, France succeeded in attracting nesting pairs to the area (Hafner 2000).

Threats
The species is threatened by wetland habitat degradation and loss (Marchant and Higgins 1990, del Hoyo et al. 1992) for example through drainage, grazing, clearing, burning, increased salinity, groundwater extraction and invasion by exotic plants (Marchant and Higgins 1990). Breeding colonies in Madagascar may be declining due to egg and chick gathering from colonies by local peoples (Langrand 1990, Kushlan and Hancock 2005) and the species previously suffered from intense persecution for the plume trade (this is no longer a threat) (del Hoyo et al. 1992).

References
Brown, L. H.; Urban, E. K.; Newman, K. 1982. The birds of Africa vol I. Academic Press, London.

Hancock, J.; Kushlan, J. 1984. The herons handbook. Croom Helm, London.

Flint, V. E.; Boehme, R. L.; Kostin, Y. V.; Kuznetsov, A. A. 1984. A field guide to birds of the USSR. Princeton University Press, Princeton, New Jersey.

Langrand, O. 1990. Guide to the birds of Madagascar. Yale University Press, New Haven, USA.

Marchant, S.; Higgins, P. J. 1990. Handbook of Australian, New Zealand and Antarctic birds, 1: ratites to ducks. Oxford University Press, Melbourne.

del Hoyo, J.; Elliot, A.; Sargatal, J. 1992. Handbook of the Birds of the World, vol. 1: Ostrich to Ducks. Lynx Edicions, Barcelona, Spain.

Snow, D. W.; Perrins, C. M. 1998. The Birds of the Western Palearctic vol. 1: Non-Passerines. Oxford University Press, Oxford.

Hafner, H. 2000. Heron nest site conservation. In: Kushlan, J. A.; Hafner, H. (ed.), Heron conservation, pp. 201-217. Academic Press, San Diego.

Kushlan, J. A.; Hancock, J. A. 2005. The herons. Oxford University Press, Oxford, U.K.

Hockey, P. A. R.; Dean, W. R. J.; Ryan, P. G. 2005. Roberts birds of southern Africa. Trustees of the John Voelcker Bird Book Fund, Cape Town, South Africa.

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

View photos and videos, and hear sounds of this species from the Internet Bird Collection

Text account compilers
Butchart, S., Ekstrom, J., Malpas, L.

IUCN Red List evaluators
Butchart, S., Symes, A.

Recommended citation
BirdLife International (2013) Species factsheet: Casmerodius albus. Downloaded from http://www.birdlife.org on 24/05/2013. Recommended citation for factsheets for more than one species: BirdLife International (2013) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 24/05/2013.

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.

To provide new information to update this factsheet or to correct any errors, please email BirdLife

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Additional resources for this species

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