Pacific reef heron

The Pacific reef heron (Egretta sacra) is a bird that lives along coastlines in southern Asia and Oceania. It is also called the eastern reef heron or eastern reef egret. This species comes in two color forms: one with slaty grey feathers and another with pure white ones. Males and females look alike.

Taxonomy

In 1789, German naturalist Johann Friedrich Gmelin formally described this heron in his updated version of Carl Linnaeus's Systema Naturae. He placed it in the genus Ardea and gave it the scientific name Ardea sacra. Gmelin based his work on the "Sacred heron," which English ornithologist John Latham had described in 1785. Naturalist Joseph Banks had given Latham a white-morph specimen collected on Tahiti.

Today, the Pacific reef heron belongs to the genus Egretta, introduced in 1817 by German naturalist Johann Reinhold Forster, which includes 12 other species. The genus name comes from the Provençal French word for little egret, aigrette, a diminutive of aigron ("heron"). The species name sacra is Latin for "sacred." Indigenous peoples across the Pacific have many names for this bird: in New Zealand, it is called kākatai, matuku moana, or matuku tai; in Fiji, belō; in Samoa, matu'u; and in Niue, Tonga, and Wallis Island, motuku.

Two subspecies are recognized. E. s. sacra ranges from coastal southern Bangladesh and the Andaman Islands to the Ryukyu Islands of southern Japan, across Australasia (excluding southern outlying islands), Melanesia (except New Caledonia), and east to the Tuamotu Archipelago in eastern Polynesia. E. s. albolineata is found only in New Caledonia, including the Loyalty Islands.

Description

These herons are medium-sized, measuring 57 to 66 centimeters long, with a wingspan of 90 to 110 centimeters and an average weight of 400 grams. The species shows an unusual color variation that is not linked to sex: some individuals are entirely white (light morph), while most are charcoal-grey (dark morph). Why this color difference exists is unknown, though camouflage is a common guess.

Young herons have browner, duller plumage. The legs are yellow-grey, and the grey morph has a narrow white stripe on its throat and chin. The beak is brown, the eyes are gold-yellow, and the face around the eyes is usually greenish to yellow.

Distribution and habitat

The Pacific reef heron is widespread across southern Asia and Oceania. In Australia, it lives along most of the coastline and on offshore islands, including the Torres Strait Islands. It is common across Micronesia, with breeding records in Guam, the Marshall Islands, the Northern Mariana Islands, and Palau, among other islands.

It also breeds throughout western Polynesia, including Fiji, French Polynesia, and Tonga, but not in Niue. Surveys of Fiji's Rotuma Island in 1991 and 2018 suggest the heron has recently colonized that island. New Zealand marks the southern limit of its range; though uncommon, the heron appears throughout the country, most often in Northland.

Breeding

Breeding occurs year-round in colonies. Nests are built in jungles, among palms and mangroves, or in cavities of old buildings, using branches and blossoms. Clutches contain two to three pale greenish-blue eggs. Both parents share brooding duties, which last about 28 days.

After hatching, the parents support the chicks for roughly five weeks. The diet consists mainly of ocean fish, crustaceans, mollusks, and worms. The heron hunts day and night, depending on the tides. During the day, it stands motionless in shallow water with its wings spread like an umbrella to reduce glare and create shade that attracts fish.

In New Zealand, the Pacific reef heron is listed as "Nationally endangered" and "Regionally Critical" in the Wellington Region.