| Citation |
BirdLife International 2016. Ardea alba. The IUCN Red List of Threatened Species 2016: e.T22697043A86468751. http://dx.doi.org/10.2305/IUCN.UK.2016-3.RLTS.T22697043A86468751.en. Downloaded on 19 September 2019. |
Description |
DESCRIPTION
Estimate includes totals for Ardea modesta. The European population of A. alba is estimated at 20,700-34,900 pairs, which equates to 41,500-69,900 mature individuals (BirdLife International 2015).
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 speciess range in North America.
HABITAT AND 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 people (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).
CONSERVATION ACTIONS
Conservation Actions Underway
The species is listed on Annex I of the EU Birds Directive, Annex II of the Bern Convention and Annex II of the Convention on Migratory Species, under which it is covered by the African-Eurasian Waterbird Agreement (AEWA).
Conservation Actions Proposed
The following information refers to the speciess European range only: 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). Freshwater habitats need to be sustainably managed. |
