Behaviour Northern populations of this species are migratory, with those breeding in the western Palearctic travelling on a broad front across the Sahara (del Hoyo et al. 1992) and those breeding in North American travelling on a narrow front along the Atlantic and Pacific coasts (Kushlan and Hancock 2005). Post-breeding southward movements occur from September to October and return northward movements occur from March to May (Kushlan and Hancock 2005). Tropical populations are not migratory but may undergo seasonal post-breeding dispersive movements (del Hoyo et al. 1992). In temperate regions breeding occurs in the local spring, with tropical and subtropical nesting generally coinciding with the rains (Kushlan and Hancock 2005). The species usually nests in small numbers (Snow and Perrins 1998) in single- or mixed-species colonies (del Hoyo et al. 1992), although sometimes groups may reach several thousand pairs (del Hoyo et al. 1992). When nesting within mixed-species colonies the species tends to form monospecific clusters (Kushlan and Hancock 2005). The species's aggregatory behaviour outside of the breeding season varies much throughout its range, some populations (e.g. in America) remaining highly gregarious throughout the year (Snow and Perrins 1998) and gathering in flocks of hundreds or even thousands to roost (del Hoyo et al. 1992), others (e.g. Palearctic breeders) being largely solitary except when roosting or on migration (Snow and Perrins 1998) (roosting flocks of 2-6 to 200 are known in Africa (Brown et al. 1992) and small flocks occur on migration) (del Hoyo et al. 1992). The species is largely crepuscular and nocturnal, but may feed diurnally especially during the breeding season (del Hoyo et al. 1992). Habitat The species inhabits fresh, brackish or saline waters with aquatic vegetation and bamboo or trees (e.g. pine, oak or mangroves) for roosting and nesting in (del Hoyo et al. 1992), showing a preference for islands or predator-free areas for nesting sites (Kushlan and Hancock 2005). It occupies the forested margins of shallow rivers, streams, lagoons, pools, ponds, lakes, marshes and mangroves and may feed on pastures, reservoirs, canals, aquaculture ponds (del Hoyo et al. 1992) and rice-fields (up to 96 % of a colony's food resources may be taken from nearby rice-fields) (Kushlan and Hancock 2005). On migration the species may also frequent dry grasslands or marine coasts (del Hoyo et al. 1992), kelp beds (Kushlan and Hancock 2005) and estuaries (Hockey et al. 2005). It breeds up to 4,800 m (Chile) (Kushlan and Hancock 2005) but is more common at elevations of up to c.2,000 m (Snow and Perrins 1998). Diet It is an opportunistic feeder taking fish, frogs, tadpoles, turtles, snakes, lizards, adult and larval insects (del Hoyo et al. 1992) (e.g. beetles, bugs, grasshoppers, crickets, flies and dragonflies) (Kushlan and Hancock 2005), spiders, crustaceans, molluscs, leeches, small rodents, bats and the eggs and chicks of other bird species (del Hoyo et al. 1992). Breeding site The nest is platform constructed of sticks and vegetation (del Hoyo et al. 1992, Kushlan and Hancock 2005) placed 2-50 m above water or on dry ground near water (Snow and Perrins 1998) in trees, bushes, reedbeds, on cliff ledges (del Hoyo et al. 1992) (overhanging rivers) (Hockey et al. 2005) and on the ground (del Hoyo et al. 1992) in protected sites (Kushlan and Hancock 2005). The species nests close together in single- and mixed-species colonies (del Hoyo et al. 1992) with as many as 20-30 pairs in the same tree (Kushlan and Hancock 2005). Colony sites may be reused in consecutive years or flocks may move to new sites (usually such movements are a result of nesting trees being destroyed due to the colony's nesting activities) (Kushlan and Hancock 2005). Colony sites are dispersed throughout the landscape in relation to distance from feeding areas (Kushlan and Hancock 2005). Management information A study carried out in north-west Italy suggests that existing nesting sites should be protected and that breeding habitats should be actively managed in order to maintain suitable habitat characteristics (Fasola and Alieri 1992). The creation of a network of new nesting sites spaced at 4-10 km in relation to available foraging habitats in zones currently without suitable nesting sites is also recommended (Fasola and Alieri 1992).

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 species's European range only: A study carried out in north-west Italy suggests that existing nesting sites should be protected and that breeding habitats should be actively managed in order to maintain suitable habitat characteristics (Fasola and Alieri 1992). The creation of a network of new nesting sites spaced at 4–10 km in relation to available foraging habitats in zones currently without suitable nesting sites is also recommended (Fasola and Alieri 1992). Measures should: Sustainably manage river valleys and reed marshes, including the reduction of water pollution and fish overexploitation and minimize disturbance from recreation at the breeding sites.