Least Bittern (Ixobrychus exilis)

Least Bittern

[order] CICONIIFORMES | [family] Ardeidae | [latin] Ixobrychus exilis | [authority] Gmelin, 1789 | [UK] Least Bittern | [FR] Petit Blongios | [DE] Amerikanische Zwergdommel | [ES] Avetorillo Panamericano | [NL] Amerikaans Woudaapje

Subspecies

Monotypic species

Genus

Ixobrychus is a genus of bitterns, a group of wading bird in the heron family Ardeidae. It has a single representative species in each of North America, South America, Eurasia and Australasia. The tropical species are largely resident, but the two northern species are partially migratory, with many birds moving south to warmer areas in winter. The Ixobrychus bitterns are all small species, their four larger relatives being in the genus Botaurus. They breed in large reedbeds, and can often be difficult to observe except for occasional flight views due to their secretive behaviour.

Physical charateristics

The Least Bittern is the smallest of all the herons.
Adult male has glossy greenish-black back. Wing coverts are pale greyish-brown, tipped with yellowish-brown. Inner secondaries are broadly edges with pale chestnut. Secondary coverts and edge of the wing at the flexure are pale chestnut. Tail is greenish-black. Buff wing coverts are visible in flight and at rest. Flight feathers are blackish.
Underparts are pale buff. It has black tufts on chest sides, usually concealed. Belly and undertail coverts are whitish.
On the head, crown is greenish-black. Sides of the head and hind neck are brownish-red or light chestnut. Chin and throat are whitish. Foreneck is pale buff, with fairly faint brown streaks.
Bill is longer than the head, about 4 cm. It is orange with dusky culmen. Lores are yellow-green. Eyes are pale yellow. Legs are greenish-yellow. Feet are yellow.
Female resembles male, but crown and mantle are dark brown, and we can see conspicuous dark streaking on underparts, and duller colours on wings.
Juvenile resembles female with paler and browner crown, and with more prominent streaking on back and crest. Bill is dusky pink to yellowish, with dark tip.
We can also find the Cory’ Least Bittern, a very rare dark morph, with dark brown colours instead brownish-red on neck, sides and front.

Listen to the sound of Least Bittern

[audio:http://www.planetofbirds.com/MASTER/CICONIIFORMES/Ardeidae/sounds/Least Bittern.mp3]

Copyright remark: Most sounds derived from xeno-canto


wingspan min.: 41 cm wingspan max.: 44 cm
size min.: 28 cm size max.: 30 cm
incubation min.: 19 days incubation max.: 20 days
fledging min.: 24 days fledging max.: 20 days
broods: 2   eggs min.: 3  
      eggs max.: 6  

Range

North America, Latin America : East, Southwest USA to Southeast Brazil

Habitat

Least Bittern lives in large marshes with dense vegetation, freshwater marshes, lakes and pools with dense fringing vegetation, but also in mangroves and brackish marshes.

Reproduction

Least Bittern nests sometimes in loose colonies. Nest is a frail platform above the water, built on bent-down, dead stalks of emergent vegetation.
Nest is built mainly by the male, and made with dead and fresh plant stems, with a canopy made with tall marsh plants pulled over the platform.
Female lays 2 to 5 bluish-white eggs, sparsely flecked with brown; incubation lasts about 19 to 20 days, shared by both parents. Particular ceremonial has been observed when adults take their turns. The bird on the nest erects its crown feathers, while calling “gra-a-a”. The other bird also fluffs crown and body feathers. When both birds are on the nest, they open their mandibles and shake their bills from side to side, with a rattling sound. This ceremonial occurs in nest relief, but also when a bird returns to the nest.
Young are fed by both adults. They are covered with rusty-brown down on back, whitish below. They fledge at about 25 days after hatching.
This species may produce two broods per season.

Feeding habits

Least Bittern feeds on small fish and aquatic invertebrates, but also on reptiles, amphibians and insects, which captures with quick jabs of its bill. It also may feed on eggs and chicks of other marsh species.

Video Least Bittern

httpv://www.youtube.com/watch?v=MmP1exzkmGY

copyright: J. del Hoyo


Conservation

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). The population trend appears to be stable, and hence the species does not 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.
Least Bittern can feed in deeper water than other herons, due to its habits of straddling reeds. It stalks preys along the reeds, sometimes in deep water, or it climbs on the reed stems, and then it strikes downwards into the water with its bill. It feeds in small pools among emergent vegetation, walking slowly at the edges of the water. It stands and waits, with legs spread apart, head and neck lowered out over the pool, and bill almost touching the water. After a capture, Least Bittern retreats back into vegetation, and moves to another pool.
Least Bittern is a shy bird. It lives an overwater life, hidden in the dense vegetation of marsh. When an intruder approaches, it runs away instead of takes off. When flushed, it moves low over the top of the emergent vegetation. It flies short distances before dropping back into vegetation.
When Least Bittern is walking or running through the vegetation, it uses plant stalks as steeping-stones. With its legs spread apart, it grasps one or several stalks with each foot, and steps along.
If alarmed or threatened, Least Bittern may freeze in place with bill pointed upright. With its brownish plumage, in this posture, it is very well camouflaged. It also may sway from side to side, following the reeds in the wind.
During courtship displays, male and female utter some sounds, one responding to the other. They are monogamous.
Least Bittern status Least Concern

Migration

Nominate exilis performs widespread post-breeding dispersal, and also long distance migration from N of range, leaving in Sept-Nov and returning in Feb-Apr, or in May in extreme N; winters from S USA through C America and Caribbean to N South America; birds from W USA migrate through W Mexico as far as Costa Rica. Migration apparently takes place by night. Straggler to N of breeding range in British Columbia and Newfoundland; accidental to Iceland and Azores. Other races seem to be sedentary, though can apparently perform some movements due to failure of seasonal rains.

Distribution map

Least Bittern distribution range map

Literature

Title Population Viability AssessmentForLeast Bittern (Ixobrychus Exilis)
Author(s): Christopher J. Whelan
Abstract: In Illinois, this species is an uncommon migrant a..[more]..
Source: Center for Biodiversity. Un. of Illinois

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Title Conservation Assessment For Least Bittern (Ixobrychus exilis)
Author(s): USDA Forest Service, Eastern Region
Abstract: This Conservation Assessment was prepared to compi..[more]..
Source: USDA Forest Service, Eastern Region

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Title The Breeding Ecology of Least Bitterns (Ixobrychus exilis) at Agassiz and Mingo
Author(s): Karen Elizabeth Arnold
Abstract: Habitat selection and reproductive effort of least..[more]..
Source: Thesis, South Dakota State University

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Title Evidence of prenuptial moult in the Little Bittern
Ixobrychus minutus
Author(s): FRANCESCO PEZZO and ANDREW G. GOSLER
Abstract: Evidence for a partial prenuptial moult in the Lit..[more]..
Source: Ringing & Migration (2005) 22, 129-132

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Title Distribution and Nesting Habitat of Least Bitterns and Other Marsh Birds in Manitoba
Author(s): STACEY HAY AND MICHELINE MANSEAU
Abstract: Call-response surveys were conducted to better del..[more]..
Source: Proc. Species at Risk 2004 Pathways to Recovery Conference

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Title Least Bittern nesting colonially
Author(s): JAMES A. KUSHLAN
Abstract: Unlike most herons, bitterns are considered to be ..[more]..
Source: The AUK, vol 90

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Title Distribution and Habitat of the Least Bittern and Other Marsh Bird Species in
Southern Manitoba
Author(s): Stacey Hay
Abstract: Call-response surveys were conducted to better del..[more]..
Source: University of Manitoba

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