Cattle egret

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Cattle egret
Breeding-plumaged adult in Wakodahatchee Wetlands.

Least Concern  (IUCN 3.1)[1]
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Aves
Order: Pelecaniformes
Family: Ardeidae
Subfamily: Ardeinae
Genus: Bubulcus
Bonaparte, 1855
Species

B. ibis (Linnaeus, 1758
)
B. coromandus
 (Boddaert, 1783)

Range of Bubulcus
  breeding
  non-breeding
  year-round

The cattle egret (Bubulcus) is a

distribution and successfully colonised
much of the rest of the world in the last century.

They are white birds adorned with buff

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

flies
from cattle and consumes them. This benefits both organisms, but it has been implicated in the spread of tick-borne animal diseases.

Taxonomy

Before the description of the Bubulcus by

sacred ibis,[5] but was applied to the western cattle egret in error.[6] The epithet coromanda refers to the Coromandel Coast of India.[6]

The eastern and western cattle egrets were split by McAllan and Bruce,

Birds of South Asia.[8] The eastern cattle egret breeds in South Asia, Eastern Asia, and Australasia, and the western species occupies the rest of the genus range, including Western Asia, Europe, Africa, and the Americas.[9] According to the IOC birdlist, they are both monotypic species. While some authorities recognise a third Seychelles subspecies, B. i. seychellarum, which was first described by Finn Salomonsen in 1934.[10]

B. i. coromandus adult showing the red flush on the legs and bill, present at the height of the breeding season

Despite superficial similarities in appearance, the cattle egret is more closely related to the genus

hybridization with little blue herons (Egretta caerulea), little egrets (E. garzetta), and snowy egrets (E. thula) have been recorded.[12]

An older English name for the cattle egret is buff-backed heron.[13]

Description

Perched on a cow in Sultanpur National Park, Haryana.
In flight near Netanya, Israel.

The cattle egret is a stocky heron with an 88–96 cm (34+1⁄2–38 in) wingspan; it is 46–56 cm (18–22 in) long and weighs 270–512 g (9+1⁄2–18 oz).[14] 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 western cattle egret 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.[15] 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.[14][16]

The eastern differs from the western 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 species' bill and tarsi are longer on average than in B. ibis.[17] B. i. seychellarum is smaller and shorter-winged than the other forms. It has white cheeks and throat, like B. ibis, but the nuptial plumes are golden, as with B. coromandus.[10] Individuals with abnormally grey, melanistic plumages have been recorded.[18][19]

The positioning of the egret's eyes allows for

crepuscular or nocturnal activity.[21] Adapted to foraging on land, they have lost the ability possessed by their wetland relatives to accurately correct for light refraction by water.[22]

Distribution and habitat

Range expansion in the Americas

The western cattle egret has undergone one of the most rapid and wide-reaching natural expansions of any bird species.[23] 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.[24] Cattle egrets were first sighted in the Americas on the boundary of Guiana and Suriname in 1877, having apparently flown across the Atlantic Ocean.[9][14] In the 1930s, the species is thought to have become established in that area.[25] It is now widely distributed across Brazil and was first discovered in the northern region of the country in 1964, feeding along with buffalos.[26]

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.[24] 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.[25] 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.[24] Breeding in the United Kingdom was recorded for the first time in 2008, only a year after an influx seen in the previous year.[27][28] In 2008, cattle egrets were also reported as having moved into Ireland for the first time.[29] 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.[30][31]

In Australia, the colonisation began in the 1940s, with the eastern cattle egret establishing itself in the north and east of the continent.[32] 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.[33]

The massive and rapid expansion of the cattle egret's

Marion Island, the South Sandwich Islands, and the South Orkney Islands.[35] A small flock of eight birds was also seen in Fiji in 2008.[36]

In addition to the natural expansion of its range, cattle egrets have been

Rodrigues, but attempts to introduce them to Mauritius failed. Numerous birds were also released by Whipsnade Zoo in England, but they were never established.[37]

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.[38]

Migration and movements

Some populations of cattle egrets are migratory, others are dispersive, and distinguishing between the two can be difficult.

sedentary and migratory. In the Northern Hemisphere, migration is from cooler climes to warmer areas, but cattle egrets nesting in Australia migrate to cooler Tasmania and New Zealand in the winter and return in the spring.[32] Migration in western Africa is in response to rainfall, and in South America, migrating birds travel south of their breeding range in the nonbreeding season.[23] Populations in southern India appear to show local migrations in response to the monsoons. They move north from Kerala after September.[39][40] During winter, many birds have been seen flying at night with flocks of Indian pond herons (Ardeola grayii) on the south-eastern coast of India[41] and a winter influx has also been noted in Sri Lanka.[8]

Young birds are known to disperse up to 5,000 km (3,000 mi) from their breeding area. Flocks may fly vast distances and have been seen over seas and oceans including in the middle of the Atlantic.[42]

Ecology and behavior

Voice

Multiple contact calls at a nighttime roost.

The cattle egret gives a quiet, throaty rick-rack call at the breeding colony, but is otherwise largely silent.[23]

Breeding

The cattle egret nests in colonies, which are often found around bodies of water.[23] The colonies are usually found in woodlands near lakes or rivers, in swamps, or on small inland or coastal islands, and are sometimes shared with other wetland birds, such as herons, egrets, ibises, and cormorants. The breeding season varies within South Asia.[8] Nesting in northern India begins with the onset of monsoons in May.[43] The breeding season in Australia is November to early January, with one brood laid per season.[44] The North American breeding season lasts from April to October.[23] In the Seychelles, the breeding season of B. i. seychellarum is April to October.[45]

The male displays in a tree in the colony, using a range of

not capable of fending for themselves; they become capable of regulating their temperature at 9–12 days and are fully feathered in 13–21 days.[48] They begin to leave the nest and climb around at 2 weeks, fledge at 30 days and become independent at around the 45th day.[47]

The cattle egret engages in low levels of brood parasitism, and a few instances have been reported of cattle egret eggs being laid in the nests of snowy egrets and little blue herons, although these eggs seldom hatch.[23] Also, evidence of low levels of intraspecific brood parasitism has been found, with females laying eggs in the nests of other cattle egrets. As much as 30% extra-pair copulations has been noted.[49][50]

The dominant factor in nesting mortality is starvation. Sibling rivalry can be intense, and in South Africa, third and fourth chicks inevitably starve.[47] In the dryer habitats with fewer amphibians, the diet may lack sufficient vertebrate content and may cause bone abnormalities in growing chicks due to calcium deficiency.[51] In Barbados, nests were sometimes raided by vervet monkeys,[9] and a study in Florida reported the fish crow and black rat as other possible nest raiders. The same study attributed some nestling mortality to brown pelicans nesting in the vicinity, which accidentally, but frequently, dislodged nests or caused nestlings to fall.[52] In Australia, Torresian crows, wedge-tailed eagles, and white-bellied sea eagles take eggs or young, and tick infestation and viral infections may also be causes of mortality.[16]

  • Cattle egret egg
    Cattle egret egg
  • Adult feeding a nestling in Apenheul zoo
    Adult feeding a nestling in
    Apenheul
    zoo
  • Juvenile on Maui (note black bill)
    Juvenile on Maui (note black bill)

Feeding

A nonbreeding adult eating a frog in the Gambia.

The cattle egret feeds on a wide range of prey, particularly

farm machinery, but it is forced to move more.[59] In urban situations, cattle egrets have also been observed foraging in peculiar situations such as railway lines.[60]

A cattle egret will weakly defend the area around a grazing animal against others of the same species, but if the area is swamped by egrets, it will give up and continue foraging elsewhere. Where numerous large animals are present, cattle egrets selectively forage around species that move at around 5–15 steps per minute, avoiding faster and slower moving herds; in Africa, cattle egrets selectively forage behind

Dominant birds feed nearest to the host, and thus obtain more food.[16]

The cattle egret sometimes shows versatility in its diet. On islands with

seabird colonies, it will prey on the eggs and chicks of terns and other seabirds.[37] During migration, it has also been reported to eat exhausted migrating landbirds.[62] Birds of the Seychelles race also indulge in some kleptoparasitism, chasing the chicks of sooty terns and forcing them to disgorge food.[63]

Threats

Pairs of crested caracaras have been observed chasing cattle egrets in flight, forcing them to the ground, and killing them.[64]

Status

B. i. seychellarum waiting for scraps at the fish market of Victoria, Seychelles.

The IUCN Red List treats them as a single species. They have a large range, with an estimated global extent of occurrence of 355,000,000 km2 (100,000,000 sq mi). Their global population is estimated to be 3.8–6.7 million individuals. For these reasons, the genus is evaluated as

least concern.[1] The expansion and establishment of the genus over large ranges has led it to be classed as an invasive species, although little, if any, impact has been noted yet.[65]

Relationship with humans

As a conspicuous genus, the cattle egret has attracted many

Arabic name, abu qerdan, means "father of ticks", a name derived from the huge number of parasites such as avian ticks found in its breeding colonies.[23][66] The Maasai people consider the presence of large numbers of cattle egrets as an indicator of impending drought and use it to decide on moving their cattle herds.[67]

The cattle egret is a popular bird with cattle

parasites such as ticks and flies.[23] A study in Australia found that cattle egrets reduced the number of flies that bothered cattle by pecking them directly off the skin.[68] It was the benefit to stock that prompted ranchers and the Hawaiian Board of Agriculture and Forestry to release the western cattle egret in Hawaii.[37][69][70]

Not all interactions between humans and cattle egrets are beneficial. The cattle egret can be a safety hazard to aircraft due to its habit of feeding in large groups in the grassy verges of airports,

Newcastle disease.[73][74]

References

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