The Cattle Egret (Bubulcus ibis) is a species of heron found in the tropics, subtropics and warm temperate zones.
The Cattle Egret is a stocky heron with a 88–96 cm (35–38 in) wingspan; it is 46–56 centimetres (18–22 in) long and weighs 270–512 grams (9.5–18.1 oz). It has a relatively short thick neck, sturdy bill, and a hunched posture. The non-breeding adult has mainly white plumage, a yellow bill and greyish-yellow legs. During the breeding season, adults 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.
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 habitatEdit
The Cattle Egret has undergone one of the most rapid and wide reaching natural expansions of any bird species. 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.
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 browsing animals, it was easily able to switch to domesticated cattle and horses. As livestock keeping spread throughout the world it 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.
The Cattle Egret nests in colonies, which are often, but not always, found around bodies of water. 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, and cormorants.
The male displays in a tree in the colony, using a range of ritualised behaviours such as shaking a twig and sky-pointing (raising bill vertically upwards), and the pair forms over three or four days. A new mate is chosen in each season and when re-nesting following nest failure. The nest is a small untidy platform of sticks in a tree or shrub constructed by both parents. Sticks are collected by the male and arranged by the female, and stick-stealing is rife. The clutch size can be anywhere from one to five eggs, although three or four is most common. The pale bluish-white eggs are oval-shaped and measure 45 mm × 53 mm. (1.8–2.1 in) Incubation lasts around 23 days, with both sexes sharing incubation duties.The chicks are partly covered with down at hatching, but are not capable of fending for themselves; they become endothermic at 9–12 days and fully feathered in 13–21 days. They begin to leave the nest and climb around at 2 weeks, fledge at 30 days and become independent at around the 45th day.
The Cattle Egret feeds on a wide range of prey, particularly insects, especially grasshoppers, crickets, flies (adults and maggots ), and moths, as well as spiders, frogs, and earthworms. The species is usually found with cattle and other large grazing and browsing animals, and catches small creatures disturbed by the mammals. Studies have shown that Cattle Egret foraging success is much higher when foraging near a large animal than when feeding singly. When foraging with cattle, it has been shown to be 3.6 times more successful in capturing prey than when foraging alone. Its performance is similar when it follows farm machinery, but it is forced to move more.
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, dominant birds feed nearest to the host, and obtain more food.