The eastern cattle egret (Bubulcus coromandus) is a species of heron (family Ardeidae) found in the tropics, subtropics and warm temperate zones. Most taxonomic authorities lump this species and the western cattle egret together as subspecies of the cattle egret, but some (including the International Ornithologists' Union) separate them. Despite the similarities in plumage to the egrets of the genus Egretta, it is more closely related to the herons of Ardea. It is native to southern and eastern Asia, and Australasia.
It is a white bird adorned with buff plumes in the breeding season. It nests in colonies, usually near bodies of water and often with other wading birds. The nest is a platform of sticks in trees or shrubs. Eastern cattle egrets exploit drier and open habitats more than other heron species. Their feeding habitats include seasonally inundated grasslands, pastures, farmlands, wetlands and rice paddies. They often accompany cattle or other large mammals, catching insect and small vertebrate prey disturbed by these animals. Some populations of the cattle egret are migratory and others show post-breeding dispersal.
The adult eastern cattle egret has few predators, but birds or mammals may raid its nests, and chicks may be lost to starvation, calcium deficiency or disturbance from other large birds. This species maintains a special relationship with cattle, which extends to other large grazing mammals; wider human farming is believed to be a major cause of their suddenly expanded range. The cattle egret removes ticks and flies from cattle and consumes them. This benefits both species, but it has been implicated in the spread of tick-borne animal diseases.
Taxonomy
Its genus name Bubulcus is Latin for herdsman, referring, like the English name, to this species' association with cattle. Ibis is a Latin and Greek word which originally referred to another white wading bird, the sacred ibis, but was applied to this species in error.
The eastern cattle egret, described by Pieter Boddaert in 1783, breeds in eastern and southern Asia and Australasia.
Despite superficial similarities in appearance, the cattle egret is more closely related to the genus Ardea, which comprises the great or typical herons and the great egret (A. alba), than to the majority of species termed egrets in the genus Egretta.
Description
The cattle egret is a stocky heron with an wingspan; it is long and weighs . It has a relatively short thick neck, a sturdy bill, and a hunched posture. The non-breeding adult has mainly white plumage, a yellow bill and greyish-yellow legs.
The eastern cattle egret differs from the western species in breeding plumage, when the buff colour on its head extends to the cheeks and throat, and the plumes are more golden in colour. The bill and tarsus are longer on average. It is also smaller and shorter-winged. It has white cheeks and throat, but the nuptial plumes are golden. The positioning of the egret's eyes allows for binocular vision during feeding, and physiological studies suggest that the species may be capable of crepuscular or nocturnal activity. Adapted to foraging on land, they have lost the ability possessed by their wetland relatives to accurately correct for light refraction by water.
This species gives a quiet, throaty rick-rack call at the breeding colony, but is otherwise largely silent.
Distribution and habitat
In Australia, colonisation began in the 1940s, with the species establishing itself in the north and east of the continent. It began to regularly visit New Zealand in the 1960s.
The expansion of the eastern cattle egret's range is due to its relationship with humans and their domesticated animals. Originally adapted to a commensal relationship with large grazing and browsing animals, it was easily able to switch to domesticated cattle and horses. As the keeping of livestock spread throughout the world, the cattle egret was able to occupy otherwise empty niches. Many populations of cattle egrets are highly migratory and dispersive, and this has helped the species' range expansion.
Although the cattle egret sometimes feeds in shallow water, unlike most herons it is typically found in fields and dry grassy habitats, reflecting its greater dietary reliance on terrestrial insects rather than aquatic prey.