Pacific reef-egret (Egretta sacra)

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White and grey morph Pacific reef-egrets on rocky shore
IUCN Red List species status – Least Concern LEAST
CONCERN

Top facts

  • The Pacific reef-egret occurs in two main colour forms, a dark morph and a white morph, although intermediate birds also occur.
  • The Pacific reef-egret has relatively short legs that give it a characteristic hunched posture.
  • A predominantly coastal species, the Pacific reef-egret is rarely found more than 100 km inland.
  • The Pacific reef-egret hunts by both day and night, timing its feeding with the tides.
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Pacific reef-egret fact file

Pacific reef-egret description

KingdomAnimalia
PhylumChordata
ClassAves
OrderCiconiiformes
FamilyArdeidae
GenusEgretta (1)

The Pacific reef-egret (Egretta sacra) is a medium-sized egret species with quite variable plumage. It occurs in two main colour morphs, one of which is all-white while the other is blue-grey to brownish-black, with white streaking on its chin and sometimes on its throat (2) (3) (4) (5). Intermediate individuals also occur (2).

During the breeding season, the Pacific reef-egret develops conspicuous, lance-shaped plumes on its neck and back (2) (4) (5). The male and female Pacific reef-egret are similar in appearance, but the male is slightly larger than the female (2) (4). Juveniles of the white morph resemble the adults, being all-white, while juveniles of the dark morph are a paler smoky-grey than the adults (2) (3) (4).

Both the male and female Pacific reef-egret have a long, thick beak, which varies from yellowish to greyish or grey-brown, sometimes with a lighter lower mandible (2) (3) (4) (5). The eyes are bright yellow, and the area between the eye and the beak is blue-grey to yellowish-green (2) (3) (4). The Pacific reef-egret has relatively short, stout legs, which give it a characteristic hunched posture. Its legs are yellow-green, greyish-yellow or brown (2) (3) (4) (5), and its feet have bright yellow soles that are conspicuous in flight (2) (4). During the breeding season, the Pacific reef-egret’s feet and beak usually become brighter yellow (2) (4), although the beak of the white morph sometimes remains a duller brownish colour (4).

There are two subspecies of Pacific reef-egret, Egretta sacra sacra and Egretta sacra albolineata, with the latter being slightly larger and often having a partly black bill. The Pacific reef-egret also varies slightly in colouration across its range. For example, dark-morph individuals from Indonesia tend to have more pronounced white streaking on the chin and throat, while those from Australia are usually darker in appearance (2) (4). Of the two colour morphs, the dark morph appears to be more common (3), with a greater proportion of dark individuals occurring in the northern and southern parts of the range. The white morph of the Pacific reef-egret tends to be more common in the tropics (2) (4).

The calls of the Pacific reef-egret include a grunting ‘ork’, given while feeding, as well as harsh croaks and squawks (2) (4), a deep ‘gruk’, and a nasal ‘gyaaah gyaaah(3).

Also known as
blue heron, blue reef heron, eastern reef egret, eastern reef heron, eastern reef-egret, Pacific reef egret, Pacific reef heron, Pacific reef-heron, reef heron.
Synonyms
Ardea sacra.
Size
Length: 58 - 66 cm (2) (3)
Wingspan: 90 - 100 cm (3)
Weight
330 - 700 g (2) (3)
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Pacific reef-egret biology

A highly territorial species, the Pacific reef-egret typically feeds alone, or sometimes in pairs or small family groups, defending a small patch of reef or shore (2) (4). However, when food is abundant it may occasionally feed in groups, and it may also roost in small groups at night, sometimes with other species (2). The Pacific reef-egret’s diet consists mainly of small fish and crabs, but it also eats insects, molluscs and even lizards (2) (4). It also takes eggs and chicks from nesting terns (2).

The Pacific reef-egret feeds both by day and by night, with the timing of its feeding depending on the tides (2) (4). This species usually hunts by walking or creeping along slowly with a distinctive, deeply crouched posture, periodically standing upright to scan for prey, or quickly chasing or lunging at it (2) (3) (4). The Pacific reef-egret may also stir the water with its feet to disturb potential prey (2) (4), and sometimes scavenges or searches under leaves on the shore (2). Some studies have suggested that the two colour morphs of the Pacific reef-egret may differ slightly in their habitat choices and feeding behaviour (2) (7).

Although the Pacific reef-egret is territorial and often nests in solitary pairs, it may also sometimes nest in small colonies (2) (4). In the northern and southern parts of its range, this species usually breeds in the spring, but in Australia and on various Pacific islands it is likely to breed year-round (2). The Pacific reef-egret’s nest is built in a sheltered site on the ground, on a ledge, among rocks, in a crevice, or in a small tree or bush. It has also been known to nest near humans, such as in a colony under a pier. The nest consists of a platform of sticks, sometimes with grass and leaf stalks mixed in (2) (4).

The female Pacific reef-egret lays a clutch of two to six greenish-blue eggs, with the average clutch size varying between different locations. Both the male and female Pacific reef-egret incubate the eggs, which hatch after 25 to 28 days (2) (4). The chicks leave the nest at about 3 weeks old (2), but they are not likely to be able to fly until they are about 40 to 50 days old (2) (4).

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Pacific reef-egret range

The Pacific reef-egret is widespread in coastal areas from Japan and Korea, through Southeast Asia to Australia and New Zealand. It also occurs on islands in the southwest Pacific (2) (3) (4) (5) (6), as far east as the Marquesas and Tuamotus Islands (2) (4). Throughout its range, the Pacific reef-egret is largely restricted to the coast, rarely being found more than 100 kilometres inland (2).

The subspecies E. s. albolineata is found on New Caledonia and the Loyalty Islands (2) (4).

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Pacific reef-egret habitat

The Pacific reef-egret is a species of the ocean shore, mainly inhabiting rocky coasts and nearby shallow reefs (2) (3) (4). It also uses mangrove-lined shores, mudflats, beaches, and tidal rivers and creeks (2) (3), although it tends to avoid sandy shores or those that are steeply shelved (4).

Although predominantly a coastal species, the Pacific reef-egret is occasionally seen slightly further inland, where it may use shallow marshland, lake edges and fields not far from the coast (2) (4).

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Pacific reef-egret status

The Pacific reef-egret is classified as Least Concern (LC) on the IUCN Red List (1).

IUCN Red List species status – Least Concern

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Pacific reef-egret threats

The Pacific reef-egret is not currently considered to be at risk of extinction, as it has a large, widespread population that is not believed to be in decline (6). However, the Pacific reef-egret may have undergone some local declines in southern Australia, Tasmania and New Zealand (2).

Potential threats to the Pacific reef-egret include human disturbance, development, habitat fragmentation, boat traffic and the effects of climate change (8).

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Pacific reef-egret conservation

In Australia, the Pacific reef-egret is given some protection as a listed marine species under the Environment Protection and Biodiversity Conservation Act 1999 (8). There are not known to be any specific conservation measures currently in place for this species in other parts of its range.

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Find out more

Find out more about the Pacific reef-egret and its conservation:

More information on conservation in Australia:

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Authentication

This information is awaiting authentication by a species expert, and will be updated as soon as possible. If you are able to help please contact:
arkive@wildscreen.org.uk

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Glossary

Incubate
To keep eggs warm so that development is possible.
Mandible
In birds, the lower jaw and beak, but the term is also used to denote the two parts of the beak.
Molluscs
A diverse group of invertebrates, mainly marine, that have one or all of the following; a horny, toothed ribbon in the mouth (the radula), a shell covering the upper surface of the body, and a mantle or mantle cavity with a type of gill. Includes snails, slugs, shellfish, octopuses and squid.
Morph
One of two or more distinct types of a given species, often distinct colour forms, which occur in the same population at the same time (that is, are not geographical or seasonal variations).
Plume
An ornamental feather that is usually long and conspicuous, and is used by a bird for display.
Subspecies
A population usually restricted to a geographical area that differs from other populations of the same species, but not to the extent of being classified as a separate species.
Territorial
Describes an animal, a pair of animals or a colony that occupies and defends an area.
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References

  1. IUCN Red List (October, 2012)
    http://www.iucnredlist.org/
  2. IUCN SSC Heron Specialist Group - Eastern reef heron (October, 2012)
    http://www.heronconservation.org/styled-5/styled-22/
  3. Brazil, M. (2009) Birds of East Asia. A&C Black Publishers, London.
  4. Hancock, J. and Kushlan, J. (2010) The Herons Handbook. A&C Black Publishers, London.
  5. McKilligan, N. (2005) Herons, Egrets and Bitterns: Their Biology and Conservation in Australia. CSIRO Publishing, Collingwood, Australia.
  6. BirdLife International - Pacific reef-egret (October, 2012)
    http://www.birdlife.org/datazone/speciesfactsheet.php?id=3713
  7. Rohwer, S. (1990) Foraging differences between white and dark morphs of the Pacific reef heron Egretta sacra. Ibis, 132(1): 21-26.
  8. Department of Sustainability, Environment, Water, Population and Communities (2012) Egretta sacra. In: Species Profile and Threats Database. Department of Sustainability, Environment, Water, Population and Communities, Canberra. Available at:
    http://www.environment.gov.au/cgi-bin/sprat/public/publicspecies.pl?taxon_id=984
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Image credit

White and grey morph Pacific reef-egrets on rocky shore  
White and grey morph Pacific reef-egrets on rocky shore

© William Osborn / naturepl.com

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