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Striated Heron

From Opus

Alternative names: Little Heron, Little Green Heron, Green-backed Heron and Mangrove Heron. Sometimes treated as conspecific with Green Heron (Butorides virescens), then taking that English name

B. s. striataPhoto by Rodrigo ConteBrasilia, Brazil, October 2012
B. s. striata
Photo by Rodrigo Conte
Brasilia, Brazil, October 2012
Butorides striata

Includes: Lava Heron

Contents

[edit] Identification

B. s. striata, juvenilePhoto by DABSDiego Martin, Trinidad, June 2016
B. s. striata, juvenile
Photo by DABS
Diego Martin, Trinidad, June 2016

Length 35-48 cm (14-18 in), wingspan 52-60 cm, weight 135-250 g.

  • Black cap
  • Whitish line from central chest to chin
  • Whitish line on central underparts, edged and/or mottled rufous in many subspecies
  • Blackish wings with greyish, dull dark greenish or brownish edging
  • Belly, flanks, neck and head are greyish to purplish-brown or buffy-brown, depending on subspecies
B. s. atricapillaPhoto by volker sthamerBilen, Ethiopia, February 2015
B. s. atricapilla
Photo by volker sthamer
Bilen, Ethiopia, February 2015
  • Yellow, bluish, or blackish lores
  • Yellowish or reddish legs, brighter when breeding
  • Yellow eyes
  • Flight low, with quick beats of wings. Neck folded, feet protrude from tail.
  • Black bill, often with yellow lower mandible

A dumpy little heron with a large head and bill. General colour blackish green; grey below; throat white; down foreneck dependent on subpecies; erectile feathers on crown, at rest extending down nape, scapulars and wing-feathers margined with white, or buffy-white ; hind-neck, sides of face, abdomen, sides of body, axillaries, and under wing-coverts grey, somewhat paler on the vent and under tail-coverts ; throat and fore-neck white with an irregular line of dark chestnut-brown feathers down the middle which spreads out and becomes pale rufous on the breast ; outer edge of wing white. Bare parts: iris yellow, deep orange when breeding; lores green to blue, yellow when breeding; bill black above, yellow green below with black tip, entirely black when breeding; feet and legs grey brown in front, yellow behind, yellow to reddish orange when breeding.

Gender can be told by colour of the legs, orange or red in males and yellow in females according to Forbes-Watson (1969)[3], though this statement has rarely been repeated.

B. s. brevipesPhoto by AlanRMuscat, Oman, January 2011
B. s. brevipes
Photo by AlanR
Muscat, Oman, January 2011

Juvenile

  • Brown
  • Whitish-buff streaking on underparts, neck and head
  • Spotting on wings
  • According to some authors the amount and intensity of the streaking on the chest is a sign of the birds age, with streaks fading with age.

Two Australian subspecies, B. s. macrorhyncha and B. s. stagnatilis, occur in both a grey and a rufous morph, while the normally grey nominate B. s. striata also occurs in a rare rufous-necked morph (confirmed for Peru and Bolivia; possibly also elsewhere).

[edit] Similar Species

Adults are generally distinctive. Rufous-necked morph of nominate race is paler, and has a greyer belly than the Green Heron (limited overlap between the two in coastal Venezuela, Trinidad & Tobago, coastal northern Colombia and eastern Panama).

Hybrids between Striated and Green Herons showing intermediate plumage have been recorded. Juveniles of Striated and Green Heron are virtually inseparable.

[edit] Distribution

B. s. javanicaPhoto by SeeTohLower Seletar Reservoir, Singapore, August 2013
B. s. javanica
Photo by SeeToh
Lower Seletar Reservoir, Singapore, August 2013

Widespread in South America (except far south and the Andes), sub-Saharan Africa (except far south), warmer parts of Asia, coastal northern and eastern Australia, and islands in the Indian Ocean and Pacific Ocean. See Subspecies, below, for further information on range. Most subspecies are sedentary or with local dispersal only, but two Asian races, B. s. amurensis and B. s. actophilus, migrate south following breeding.

Generally common and widespread. Some localised subspecies are rarer, and it has been estimated that only around 100 individuals remain of the subspecies B. s. patruelis.

[edit] Taxonomy

B. s. macrorhyncha (grey morph)Photo by kerriebrGold Coast, Queensland, Australia, September 2013
B. s. macrorhyncha (grey morph)
Photo by kerriebr
Gold Coast, Queensland, Australia, September 2013

The scientific name was recently corrected from Butorides striatus to Butorides striata. This species was previously sometimes placed in the genus Ardeola.

[edit] Subspecies

Very variable, with 21-22 subspecies currently accepted:

[edit] American subspecies

  • B. s. striata

[edit] African and Middle East subspecies

  • B. s. atricapilla
  • Africa south of the Sahara. Streaks on the throat tawny rufous. Grey ornamental plumes on the back, wing coverts edged with sandy buff, crown is greenish black. Upper mandible dusky, lower mandible greenish yellow with dusky margins. Iris light yellow.
  • B. s. brevipes
  • Somalia and the Red Sea and Arabian coasts.

[edit] Indian Ocean subspecies

B. s. macrorhyncha (rufous morph)Photo by NeilNarrabeen, Sydney, New South Wales, Australia, July 2003
B. s. macrorhyncha (rufous morph)
Photo by Neil
Narrabeen, Sydney, New South Wales, Australia, July 2003
  • B. s. rutenbergi
  • B. s. rhizophorae
  • B. s. crawfordi
  • Aldabra Islands and Amirante Islands.
  • B. s. degens
  • B. s. albolimbata (syn. B. s. albidula, B. s. didi)
  • B. s. spodiogaster
  • Andaman Islands, Nicobar Islands, and islands off western Sumatra. Throat and cheek-stripe ashy or brown, not distinctly indicated, abdomen rusty. Sides of neck and sides of body dark, sooty, slate colour; cheeks and ear coverts also slate colour. Bill black, lower portion of lower mandible, from base to tip, edged pale horny.

[edit] Asian subspecies

  • B. s. amurensis
  • Southeast Siberia, northeast China, Japan; migrates south to Sumatra and Philippines in winter. As B. s. javanicus but stockier and longer-winged (wing 17-22 cm, compared to 17 cm for B. s. javanicus) and with a coarser bill.
  • B. s. actophila
  • Eastern China to Myanmar and northern Vietnam; migrates south to Sumatra, Borneo, and Nicobar Islands in winter.
  • B. s. javanica (syn. B. s. chloriceps, B. s. carcinophila)
  • Pakistan, India, Sri Lanka, Thailand, Philippines, Greater Sundas, Sulawesi. Throat and foreneck uniform or mottled with blackish, but never streaked with tawny rufous. Plumes with white-shaft lines, scapular feathers green, sometimes with grey tips. Wing coverts green with buff margins. Below the eye there is a streak of greenish black extending along the ear coverts, edged with a white streak on the top, a second streak from the lower mandible along the cheeks. Upper mandible black with longitudinal yellow stripe below the nostrils. Facial skin and legs green.
B. s. sundevalli (Lava Heron)Photo by bionicsherpaJames Island, Galapagos, March 2009
B. s. sundevalli (Lava Heron)
Photo by bionicsherpa
James Island, Galapagos, March 2009

[edit] Australasian subspecies

  • B. s. steini
  • B. s. moluccarum
  • B. s. papuensis
  • B. s. idenburgi
  • Northern New Guinea.
  • B. s. flyensis
  • South central and southeast New Guinea.
  • B. s. macrorhyncha (syn. B. s. littleri)
  • B. s. stagnatilis (syn. B. s. cinerea, B. s. rogersi)
  • Northern Australia. Sides of neck washed with rusty brown like the sides of the body, abdomen, cheeks and ear coverts rusty brown.
  • B. s. patruelis
  • B. s. solomonensis

[edit] Galapagos subspecies

  • B. s. sundevalli
  • Galapagos. Treated as a separate species Lava Heron Butorides sundevalli by several authorities. Entire plumage dark grey to blackish.

The monophyly of all subspecies of Striated Heron with respect to Green Heron is yet to be established. Some authorities include Green Heron as a further subspecies to avoid this question; others have suggested that Striated Heron may be split into several species in the future.

[edit] Habitat

The species shows a preference for forested water margins such as mangrove-lined shores and estuaries, or dense woody vegetation fringing ponds, rivers, lakes and streams. Other suitable habitats include river swamps, canals, artificial ponds, salt-flats, mudflats, tidal zones, exposed coral reefs, reedbeds, grassy marshland, pastures, rice-fields and other flooded cultivation. In plains to an altitude of 750m, occasionally up to 1300m. There have also been a few records in savannah woodland, where the bird would hunt tadpoles in shallow pools, far away from permanent water.

[edit] Behaviour

This species is extremely territorial and often forages and nests alone, occasionally in good conditions the birds nest in loosely spaced groups of 5-15 pairs, or even more rarely, in very large groups of several hundred pairs. This territoriality extends to their foraging behaviour, where birds will stand on floating debris, hunting for trapped insects, until the debris leaves their immediate territory, at which they will return to the bank. Often seen watching water from a shallow perch for food, also sometimes in rice fields. When hunting the birds will occasionally use 'bait' dropping a feather or leaf on the water and spearing the fish that come to investigate. There have also been reports of birds dropping bread scraps in the water. Another interesting foraging technique is using a floating piece of debris as a 'base' from which they can float into deeper water, and have been observed diving into the water to a considerable depth in order to catch a fish. Although they forage throughout the day their activity spikes in the evening and morning. They nest near water in broadleaf forest or shrub canopy shelter. Young Birds will occasionally give a display if threatened, which consists of stretching their neck, and pointing their bill up. An additional threat display is detailed and illustrated here. Adults will freeze when disturbed; standing motionless with their bills at 45°. Often relatively tame around inhabited areas.

[edit] Diet

Diet is mainly fish, frogs, snails and insects, though stomach content analysis contained fragments of Limnocharis (A common wetland plant) and insect fragments

[edit] Breeding

The breeding season varies according to the location, but in the tropics occurs during heavy rains. Nest is a small, shallow structure of twigs, placed hidden among the braches of trees and shrubs (especially mangroves Rhizophora spp. and Avicennia spp., but also other trees) between 0.3 and 10 m above the water, ridiculously small for the bird, normally being a few dry sticks put together. Clutch of 3-5 eggs, both the male and female co-incubate, through a period of 20-22 days. Eggs are pale blue and measure 36x28mm. In China the breeding season is April to September, wintering around the coastal areas of Jiangsu, but numbering less than one hundred.

[edit] References

  1. Clements, J. F., T. S. Schulenberg, M. J. Iliff, D. Roberson, T. A. Fredericks, B. L. Sullivan, and C. L. Wood. 2015. The eBird/Clements checklist of birds of the world: v2015, with updates to August 2015. Downloaded from http://www.birds.cornell.edu/clementschecklist/download/
  2. Gill, F and D Donsker (Eds). 2015. IOC World Bird Names (version 5.3). Available at http://www.worldbirdnames.org/.
  3. Forbes-Watson, A. D. (1969). Notes on birds observed in the Comoros on behalf of the Smithsonian Institution. Atoll Research Bulletin 128.

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