- Ardea stellaris Linnaeus, 1758
Eurasian Bittern, Bittern, Common Bittern, Eurasian Bittern
Be (II); Bo (AEWA); EUBD (I)
Value of species
A European Union International Action Plan for the Conservation of this species was published in 1996 (Newbery et al. 1996).
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). Despite the fact that the population trend appears to be decreasing, the decline is not believed to be sufficiently rapid to approach the thresholds for Vulnerable 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.
The global population is estimated to number c.115,000-340,000 individuals (Wetlands International 2015). The European population is estimated at 37,600-66,400 calling or lekking males, which equates to 75,300-133,000 mature individuals (BirdLife International 2015). National population estimates include: c.100-10,000 breeding pairs, c.50-1,000 individuals on migration and c.50-1,000 wintering individuals in China; < c.1,000 wintering individuals in Korea; < c.100 breeding pairs and < c.50 wintering individuals in Japan and < c.100,000 breeding pairs and < c.1,000 individuals on migration in Russia (Brazil 2009).
Trend Justification: The overall population trend is decreasing, although some populations have unknown trends and others are stable (Wetlands International 2015). The European population is estimated to be stable (BirdLife International 2015).
Behaviour Populations breeding on the Atlantic coast of Europe, in the Mediterranean and in South Africa are largely sedentary due to the relatively mild winters (Newbery et al. 1996) (although they may make local dispersive movements related to rainfall) (Hancock and Kushlan 1984). Continental populations are mainly migratory however (Newbery et al. 1996, Kushlan and Hancock 2005) with a marked post-breeding dispersal of immatures (Kushlan and Hancock 2005). The species breeds from March to June in Eurasia and during the rains from September to January in South Africa (del Hoyo et al. 1992). It usually nests solitarily although males are polygamous and may mate with up to five females nesting on a large wetland site (del Hoyo et al. 1992). The species remains solitary throughout the year (del Hoyo et al. 1992) (although migratory individuals may travel in small flocks) (Kushlan and Hancock 2005), and is mainly crepuscular in its activities (Kushlan and Hancock 2005). Habitat Breeding The species has highly restrictive breeding habitat requirements (del Hoyo et al. 1992). It shows a strong preference for quiet lowland marshes around lakes and rivers (less than 200 m above sea-level) (Kushlan and Hancock 2005) with extensive dense young reedbeds of Phragmites spp. (e.g. with 1- 3 years worth of new growth (Marion et al. 2000, Puglisi et al. 2005) but still maintaining some old or dead stems (del Hoyo et al. 1992)) that are flooded but are fairly shallow (del Hoyo et al. 1992) (less than 30 cm deep) (Newbery et al. 1996), have few fluctuations in water-level (del Hoyo et al. 1992), have low acidity (Kushlan and Hancock 2005)and are surrounded by clear open areas (del Hoyo et al. 1992) of deeper water is maintained into the driest part of the breeding season (Gilbert et al. 2005). Breeding adults are more attracted to unfragmented (Puglisi et al. 2005) reedbeds over 20 ha in area, although smaller sites with networks of reed-fringed waterways or open wetland habitats with a number of small reedbeds (Newbery et al. 1996) (greater than 100 m) (Gilbert et al. 2005) over a wide area may also be used (Newbery et al. 1996). The species avoids saline waters (Kushlan and Hancock 2005) but is equally abundant in fresh or brackish habitats (del Hoyo et al. 1992) (e.g. in estuarine or delta marshes) (Snow and Perrins 1998), and may occasionally nest in stands of rushes Scirpus spp. (del Hoyo et al. 1992) or Papyrus spp. if reeds are unavailable (Kushlan and Hancock 2005). Non-breeding The species frequents a more varied range of habitats outside of breeding season, foraging on rice-fields, watercress beds, gravel pits, fish farms, ditches, sewage farms (del Hoyo et al. 1992), small ponds and wet grassy areas (Kushlan and Hancock 2005) as well as marshes and reedbeds (del Hoyo et al. 1992). It also forages in running water (e.g. streams) when still waterbodies freeze during the winter (Hancock and Kushlan 1984). Diet Its diet varies depending on the site and season although it predominantly takes fish (particularly cyprinids and eels) and amphibians as well as adult and larval insects, spiders, crustaceans, molluscs, snakes, lizards, birds, nestlings and small mammals (del Hoyo et al. 1992). Breeding site The nest is a pad of reeds and other vegetation (Kushlan and Hancock 2005) constructed close to or floating on water (del Hoyo et al. 1992) amidst dense reedbeds (del Hoyo et al. 1992, Kushlan and Hancock 2005). Although it is a solitary nester, breeding densities from 2 per 100 ha to 100 per 100 ha may occur depending on the quality of the habitat (Kushlan and Hancock 2005), nests sometimes being placed close together in areas where the species is particularly numerous (Hancock and Kushlan 1984). Management information Breeding adults in Europe may be more attracted to unfragmented (Puglisi et al. 2005) reedbeds over 20 ha in area, although smaller sites with networks of reed-fringed waterways or open wetland habitats with a number of small reedbeds over a wide area may also be used (Newbery et al. 1996). There is evidence that females in Britain preferentially nest in locations surrounded by less scrub but more vegetated open water, with a higher proportion of Phragmites spp. than other plant species, and in areas where deeper water is maintained into the driest part of the breeding season (Gilbert et al. 2005). The European Action Plan for this species recommends raising water levels, harvesting and burning reeds, cutting invasive scrub, or digging out reedbeds on a rotational compartmental basis as methods of slowing reedbed succession (Newbery et al. 1996). It also recommends the regular cutting of small areas of reedbed to maintain Phragmites spp. monocultures (Newbery et al. 1996), to provide a range of multi-age reed stands (Kushlan and Hancock 2005) and to favour the retention of water levels in spring and summer (promoting rapid growth, preventing a build-up of reed litter and providing foraging sites) (Newbery et al. 1996). Large-scale reed cutting should be prohibited in the late-winter however (Kushlan and Hancock 2005). Wetlands should also be managed to enhance the carrying capacity of fish and eel populations (thus increasing food resources for bitterns) (Noble et al. 2004, Self 2005, Gilbert et al. 2007). In Britain it was found that suitable habitats should be provided for all fish life stages (including spawning, refuge and overwintering), the movement of fish throughout reedbeds should be promoted (e.g. by changes in hydrological management regimes and sluice design) (Noble et al. 2004) and issues relating to water quality, zooplankton and macrophyte community structures should be addressed (Self 2005).
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