Populations breeding in the western Palearctic are migratory (Billerman et al. 2020) and travel on a broad front between breeding and wintering grounds (Kushlan and Hancock 2005). The species breeds from April to June in the western Palearctic. It is a colonial breeder (Hancock and Kushlan 1984, Billerman et al. 2020, Turner 2000, Kushlan and Hancock 2005) and although nesting group sizes are usually small and rarely exceed 50 pairs (Turner 2000), colonies of up to 1,000 pairs have been recorded in some areas (Hancock and Kushlan 1984, Billerman et al. 2020). It often also nests on the periphery of colonies of other heron species such as Grey Heron (Ardea cinerea) (Kushlan and Hancock 2005). In migratory populations the autumn migration occurs from August to October (Hancock and Kushlan 1984), with the return passage in the spring beginning in March (Hancock and Kushlan 1984). The species is mainly crepuscular, but may also feed diurnally. The species inhabits wetlands from sea level to 1,800 m (Billerman et al. 2020), showing a preference for dense, flooded, freshwater reedbeds (Phragmites spp.) in temperate areas (occupying Typha, Scirpus and Papyrus swamps elsewhere) (Kushlan and Hancock 2005). It also utilises lake shores, river margins (Billerman et al. 2020), ditches, canals, brackish water lagoons (Kushlan and Hancock 2005), rice-fields and coastal mudflats (Billerman et al. 2020). Its diet consists of fish 5–15 cm long (Billerman et al. 2020) (occasionally up to 55 cm), salamanders (Kushlan and Hancock 2005), frogs, insects (Billerman et al. 2020) (e.g. beetles, dragonflies, hemiptera (Kushlan and Hancock 2005) and locusts (Hancock and Kushlan 1984)), crustaceans (Billerman et al. 2020), spiders (Kushlan and Hancock 2005) and molluscs (Hancock and Kushlan 1984) as well as small birds and mammals, snakes and lizards (Billerman et al. 2020). The nest is a platform of reeds stems or sticks (Kushlan and Hancock 2005) positioned over or beside water up to three metres high in flooded reedbeds (Billerman et al. 2020), three to four metres high in thickets (Kushlan and Hancock 2005) or up to 25 m high in trees (Billerman et al. 2020). The species usually nests in loose single- or mixed-species colonies with A. cinerea, and although colony sizes are usually small, large groups of up to 1,000 pairs have been recorded (Hancock and Kushlan 1984, Billerman et al. 2020).

Although the generation length for both EU and Europe regional assessments were calculated using the same methodology, new information arriving after the EU assessments were undertaken gave rise to an update in the generation lengths. This new information was then used for the Europe level assessments giving rise to a difference between the generation lengths used for the EU and Europe regions.

In Europe, this species breeds notably in Ukraine, Russia, Romania, Spain, France and Italy.

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
Studies in southern France have shown that the overall conservation of this species in Europe is favoured by maintaining large uncut reedbeds with relatively high spring water levels (Barbraud et al. 2002). Freshwater habitats need to be sustainably managed and non-intrusion zones established around colonies.