cattle egrets

The cattle egret (''Bubulcus ibis'') is a cosmopolitan species of heron (family Ardeidae) found in the tropics, subtropics, and warm-temperate zones. It is the only member of the monotypic genus ''Bubulcus'', although some authorities regard its two subspecies as full species, the western cattle egret and the eastern cattle egret. Despite the similarities in plumage to the egrets of the genus ''Egretta'', it is more closely related to the herons of ''Ardea''. Originally native to parts of Asia, Africa, and Europe, it has undergone a rapid expansion in its distribution and successfully colonised much of the rest of the world in the last century.

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. 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 are migratory and others show postbreeding dispersal.

The adult 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

The cattle egret was first described in 1758 by Carl Linnaeus in his ''Systema Naturae'' as ''Ardea ibis'', but was moved to its current genus by Charles Lucien Bonaparte in 1855. Its generic 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 cattle egret has two geographical races, which are sometimes classified as full species, the western cattle egret, ''B. ibis'', and eastern cattle egret, ''B. coromandus''. The two forms were split by McAllan and Bruce, but were regarded as conspecific by almost all other recent authors until the publication of the influential ''Birds of South Asia''. The eastern subspecies ''B. i. coromandus'', described by Pieter Boddaert in 1783, breeds in South Asia, Eastern Asia, and Australasia, and the western nominate form occupies the rest of the species range, including Western Asia, Europe, Africa, and the Americas. Some authorities recognise a third Seychelles subspecies, ''B. i. seychellarum'', which was first described by Finn Salomonsen in 1934.

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''. Rare cases of hybridization with little blue herons (''Egretta caerulea''), little egrets (''E. garzetta''), and snowy egrets (''E. thula'') have been recorded.

An older English name for the cattle egret is buff-backed heron.

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 nonbreeding adult has mainly white plumage, a yellow bill, and greyish-yellow legs. During the breeding season, adults of the nominate western subspecies develop orange-buff plumes on the back, breast, and crown, and the bill, legs, and irises become bright red for a brief period prior to pairing. The sexes are similar, but the male is marginally larger and has slightly longer breeding plumes than the female; juvenile birds lack coloured plumes and have a black bill.

''B. i. coromandus'' differs from the nominate subspecies in breeding plumage, when the buff colour on its head extends to the cheeks and throat, and the plumes are more golden in colour. This subspecies' bill and tarsi are longer on average than in ''B. i. ibis''. ''B. i. seychellarum'' is smaller and shorter-winged than the other forms. It has white cheeks and throat, like ''B. i. ibis'', but the nuptial plumes are golden, as with ''B. i. coromandus''. Individuals with abnormally grey, melanistic plumages have been recorded.

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.

Distribution and habitat

The cattle egret has undergone one of the most rapid and wide-reaching natural expansions of any bird species. It was originally native to parts of southern Spain and Portugal, tropical and subtropical Africa, and humid tropical and subtropical Asia. At the end of the 19th century, it began expanding its range into southern Africa, first breeding in the Cape Province in 1908. Cattle egrets were first sighted in the Americas on the boundary of Guiana and Suriname in 1877, having apparently flown across the Atlantic Ocean. In the 1930s, the species is thought to have become established in that area. It is now widely distributed across Brazil and was first discovered in the northern region of the country in 1964, feeding along with buffalos.

The species first arrived in North America in 1941 (these early sightings were originally dismissed as escapees), bred in Florida in 1953, and spread rapidly, breeding for the first time in Canada in 1962. It is now commonly seen as far west as California. It was first recorded breeding in Cuba in 1957, in Costa Rica in 1958, and in Mexico in 1963, although it was probably established before then. In Europe, the species had historically declined in Spain and Portugal, but in the latter part of the 20th century, it expanded back through the Iberian Peninsula, and then began to colonise other parts of Europe, southern France in 1958, northern France in 1981, and Italy in 1985. Breeding in the United Kingdom was recorded for the first time in 2008, only a year after an influx seen in the previous year. In 2008, cattle egrets were also reported as having moved into Ireland for the first time. This trend has continued and cattle egrets have become more numerous in southern Britain with influxes in some numbers during the nonbreeding seasons of 2007/08 and 2016/17. They bred in Britain again in 2017, following an influx in the previous winter, and may become established there.

In Australia, the 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. Since 1948, the cattle egret has been permanently resident in Israel. Prior to 1948, it was only a winter visitor.

The massive and rapid expansion of the 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. The species has been seen as a vagrant in various sub-Antarctic islands, including South Georgia, Marion Island, the South Sandwich Islands, and the South Orkney Islands

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