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Botaurus stellarisEurasian bittern(Also: great bittern)

By Ethan Graves

Geographic Range

The Great Bittern is found breeding throughout temperate Western Europe as far south as the Mediterranean, across the temperate parts of Eurasia and Asia into Japan. Great bitterns winter in Central and South Africa, South-East Asia, and the Southern Mediterranean coast. Bitterns can be found year round in the British Isles and Netherlands (White et al. 2006) (White, et al., 2006)

Habitat

The Eurasian Bittern (Botaurus stellaris) or Great Bittern (henceforth: bittern) is an elusive bird which is rarely seen. The bittern prefers reed beds (Phragmites or Typha), rice-fields, saw-sedge, or marsh/wetland vegetation types in the early stages of succession. These vegetation types provide thick cover to protect the bitterns nest, an elevated platform which it weaves into the standing vegetation. Habitats that provide early succession marshes and mires flood early in the spring and gradually drain over the summer, when these habitats are flooded they provide the bittern with adequate food resources, visual concealment, and protection from ground predators. Females seem to choose nesting sites where the water remains relatively deeper during the dry period of the summer than the surrounding area. Reed beds within wetlands whose depth gradually tapers from 10-40 cm, that also border, deeper, relatively less vegetated waters provide optimal fishing habitat for bitterns (Cramp & Simmons 1977, Puglisi & Bretagnolle 2005, White et al. 2006, Polak 2007). (Cramp and Simmons, 1977; Polak, 2007; Puglisi and Bretagnolle, 2005; White, et al., 2006)

Physical Description

The bittern is a mid-sized reclusive marsh-bird in the heron family. Bitterns show a great deal of phenotypic plasticity through body size across its range. Individual size may vary depending on available food or weather conditions.

Two subspecies are recognized; the northern race (B. s. stellaris) found throughout Europe and Asia, and (B. s. capensis) which resides year round in South Africa (Cramp & Simmons 1977, White et al. 2006). (Cramp and Simmons, 1977; White, et al., 2006)

  • Sexual Dimorphism
  • male larger
  • Range mass
    874 to 243 g
    30.80 to 8.56 oz
  • Range length
    64 to 80 cm
    25.20 to 31.50 in
  • Range wingspan
    125 to 135 cm
    49.21 to 53.15 in

Reproduction

Male bitterns exhibit polygyny in which males mate with more than one female. Males produce deep vocalizations during the breeding season to communicate physical fitness and attract a mate. These vocalizations are known as "booms" and the sound can carry for up to 4 Km (Puglisi & Adamo 2004, White et al. 2006). (Puglisi and Adamo, 2004; White, et al., 2006)

Bitterns are polygynous breeders in which solitary males will attract females with a song “boom” in order to encourage copulation. Bitterns lay their eggs asynchronously, with 1-2 days between individual egg layings. The disparity in development across the brood due to the asynchronous egg laying likely contributes to the mortality of nearly every chick that hatched last of its brood which is out-competed by its siblings for resources in the nest (Puglisi & Bretagnolle 2005, White et al. 2006, Zbigniew et al. 2014). (Puglisi and Bretagnolle, 2005; White, et al., 2006; Zbigniew, et al., 2014)

  • Breeding interval
    Great bitterns typically rear a brood once yearly sometime in late March to early June, though individuals have been observed rearing a second brood following the failure of a first brood
  • Breeding season
    Bitterns lay their eggs between March 25-June 20, with possible second brood dependent on first brood timing and habitat favorability, a second brood often follows a nest failure (Puglisi & Bretagnolle 2005, White et al. 2006)
  • Range eggs per season
    3 to 6
  • Average eggs per season
    4.2
  • Average time to hatching
    25 +/- 1.24 days
  • Average fledging age
    15 days
  • Range time to independence
    50 to 55 days

Of the two sexes, female bitterns invest the majority of the parental workload. Once copulation is complete the role of the male bittern as a mate is over. Females are left to build their nests, incubate their eggs and nourish their brood without the assistance of a mate. Female bitterns will periodically leave the nest to hunt for fish in the waters surrounding the nest site to provide food for her offspring. The most common causes of nest mortality are starvation and nest depredation. Protection from nest depredation and food abundance are both positively associated with the preferred depth of water which the great bittern will build its nest. In cases where food is scarce in proximity to the nest site breeding female bitterns will fly out of the nesting territory in search of food, leaving the chicks more susceptible to depredation (Cramp & Simmons 1977, Voisin 1991, White et al. 2006, Polak 2007). (Cramp and Simmons, 1977; Polak, 2007; White, et al., 2006)

Lifespan/Longevity

Little information is available on the lifespan and longevity of the great bittern either in captivity or in the wild.

Behavior

The Eurasian bittern is a master of stealth and camouflage. Its plumage of streaked brown, grey, and black allow the bittern to blend in with its surroundings. When startled the bittern extends its neck and body such that the streaks on its body parallel the surrounding vegetation, the bittern can even sway parts of its body to cast the illusion of reeds blowing in the wind. A skilled fisher, the bittern often approaches a fishing spot disguising its presence by leading with its camouflaged neck until an opportune time to spear/catch a prey item arises (White et al. 2006). (White, et al., 2006)

  • Range territory size
    200000 (low) m^2

Home Range

The exact home range of an individual bittern can vary widely depending on the food availability at a given site. A site with high quality food production could be of relatively small size to a site with poorer food production and produce the same nutritional value to the individual (Polak 2007). (Polak, 2007)

Communication and Perception

The only vocalizations occurring in the great bittern is the "boom". Booming is the name given to the deep vocalization made by male bitterns during the breeding season. To produce this low sound the bittern forces its esophagus full of air and physically produces resonance between its neck and its air-filled esophagus (Puglisi & Adamo 2004). (Puglisi and Adamo, 2004)

Food Habits

Bitterns are very reclusive and thus rely on food sources in the waters of their reedbed habitats. Bitterns prefer to fish in shallow waters that gradually deepen and lack steep and abrupt sides. Common shallow/ephemeral water representatives like fish, crustaceans, amphibians and insects make up the majority of the bittern’s diet. Few varieties of indigenous fish that actually penetrate into the reed beds occur alongside the bittern which, if absent or relatively absent from a territory, may cause the female to forage outside of the nesting territory (Cramp & Simmons 1977, Alesandria et al. 2003, Gilbert et al. 2003, Puglisi & Bretagnolle 2005, White et al. 2006). (Cramp and Simmons, 1977; Puglisi and Bretagnolle, 2005; White, et al., 2006)

  • Animal Foods
  • amphibians
  • fish
  • insects
  • aquatic crustaceans

Predation

Bitterns have cryptic plumage which keeps them concealed in their habitat. Bitterns are adapted to elongate their neck and body, such that they appear to be reeds swaying in the wing. Bittern nests suffer mortality for generally two reasons, starvation and depredation upon the nest. One of the most beneficial things a bittern can do to prevent depredation is to build the nest in a safe place. The nests are inconspicuously woven of the surrounding materials. The placement of the nest often is above water such that predators are deterred. Bittern chicks are adapted to leave the nests alone as young as two weeks old if they sense danger while the mother is gone (White et al. 2006, Zbigniew et al. 2014). (White, et al., 2006; Zbigniew, et al., 2014)

  • Anti-predator Adaptations
  • cryptic

Ecosystem Roles

Due to the widespread distribution and abundance of the Eurasian bittern, the ecosystem role it plays is one of an umbrella species. Protecting habitats that bitterns live in ultimately benefits countless other species in the process. (Cramp and Simmons, 1977)

Economic Importance for Humans: Positive

Conserving habitat for Botaurus stellaris is important as it is an umbrella species with a vast distribution and a life history that crosses paths with many other marsh/mire guilds. (White, et al., 2006)

Economic Importance for Humans: Negative

There are no known adverse effects of Botaurus stellaris on humans. (Longoni, 2010; Polak, et al., 2008; White, et al., 2006)

Conservation Status

The abundance and distribution of the bittern is vast, so vast in fact that the degradation of its habitat and slow downward trajectory of its population seems to go largely unnoticed. As many marshes and wetlands are converted from their natural state, indigenous animals are left to look elsewhere to satisfy their needs. The bittern has taken to rice fields in Great Britain in lieu of its ideal wetland conditions. Though rice fields work for breeding, they are lower in food quality and breeding birds using these sites have a much later fledging time than those raised in traditional habitats. (Longoni, 2010; Polak, et al., 2008; White, et al., 2006)

Contributors

Ethan Graves (author), University of Wisconsin - Stevens Point, Christopher Yahnke (editor), University of Wisconsin-Stevens Point, Tanya Dewey (editor), University of Michigan-Ann Arbor.

Glossary

Ethiopian

living in sub-Saharan Africa (south of 30 degrees north) and Madagascar.

World Map

Palearctic

living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.

World Map

acoustic

uses sound to communicate

agricultural

living in landscapes dominated by human agriculture.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

cryptic

having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.

ecotourism

humans benefit economically by promoting tourism that focuses on the appreciation of natural areas or animals. Ecotourism implies that there are existing programs that profit from the appreciation of natural areas or animals.

endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

female parental care

parental care is carried out by females

insectivore

An animal that eats mainly insects or spiders.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

marsh

marshes are wetland areas often dominated by grasses and reeds.

migratory

makes seasonal movements between breeding and wintering grounds

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

oriental

found in the oriental region of the world. In other words, India and southeast Asia.

World Map

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

piscivore

an animal that mainly eats fish

polygynous

having more than one female as a mate at one time

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

tropical savanna and grassland

A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.

savanna

A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.

temperate grassland

A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.

visual

uses sight to communicate

References

Adamo, C., L. Puglisi, E. Baldaccini. 2004. Factors affecting Bittern Botaurus stellaris distribution in a Mediterranean wetland. Bird Conservation international, 14: 153-164. Accessed May 01, 2016 at https://www.researchgate.net/profile/Luca_Puglisi/publication/248693034_Factors_affecting_Bittern_Botaurus_stellaris_distribution_in_a_Mediterranean_wetland/links/0046352f9518f19269000000.pdf.

Cramp, S., K. Simmons. 1977. Handbook of the Birds of Europe, the Middle East, and North Africa: The Birds of the Western Palearctic. Oxford, United Kingdom: Oxford University Press.

Demongin, L., M. Dmitrenok, V. Bretagnolle. 2007. Determining great bittern Botaurus stellaris laying date from egg and chick biometrics. Bird Study, 54(1): 54-60.

Dmitrenok, M., L. Puglisi, L. Demongin, G. Gilbert, M. Polak, V. Bretagnolle. 2007. Geographical variation, sex and age in Great Bittern Botaurus stellaris using coloration and morphometrics. Ibis, 149: 37-44.

Longoni, V. 2010. Rice Fields and Waterbirds in the Mediterranean Region and the Middle East. Waterbirds, 33 (Special Publication 1): 83-96. Accessed May 01, 2016 at http://www.bioone.org/doi/full/10.1675/063.033.s106.

Polak, M. 2007. Nest-Site Selection and Nest Predation in the Great Bittern Botaurus stellaris Population in Eastern Poland. Ardea, 95(1): 31-38.

Polak, M., Z. Kasprzykowski, M. Kucharczyk. 2008. Micro-habitat nest preferences of the great bittern, Botaurus stellaris, on fishponds in central-eastern Poland. Annales Zoologici Fennici, 45: 102-108.

Puglisi, L., C. Adamo. 2004. Discriminatinon of individual voices in male great bittern (Botaurus stellaris) in Italy. The Auk, 121 (2): 541-547. Accessed May 01, 2016 at http://www.bioone.org/doi/full/10.1642/0004-8038%282004%29121%5B0541%3ADOIVIM %5D2.0.CO%3B2.

Puglisi, L., V. Bretagnolle. 2005. Breeding Biology of the Great Bittern. Waterbirds, 28(3): 392-398. Accessed May 01, 2016 at http://www.bioone.org/doi/full/10.1675/1524-4695%282005%29028%5B0392%3ABBOTGB%5D2.0.CO%3B2.

White, G., J. Purps, S. Alsbury. 2006. The bittern in Europe: a guide to species and habitat management. The Lodge, Sandy, Bedfordshire: The Royal Society for the Protection of Birds.

Zbigniew, K., M. Polak, P. Chylarecki. 2014. Effects of Weather Conditions, Time of Breeding, Brood Size and Hatching Order on Eurasian Bittern Nestling Growth in a Food-Rich Fishpond Habitat. Annales Zoologici Fennici, 51(6): 477-487. Accessed May 01, 2016 at http://www.bioone.org/doi/full/10.5735/086.051.0602.

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