The Cattle Egret nests in colonies, which are often, but not always,
found around b odies
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,
ibises and cormorants.
The male displays in a tree in the colony, using an 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 x
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 engages in low levels of brood parasitism, and there
are a few instances of Cattle Egret eggs being laid in the nests of
Snowy Egrets and Little Blue Herons, although these eggs seldom
hatch.[19] There is also evidence of low levels of intraspecific brood
parasitism, with females laying eggs in the nests of other Cattle
Egrets. As much as 30% extra-pair copulations have been noted.
The dominant factor in nesting mortality is starvation. Sibling rivalry
can be intense, and in South Africa third and fourth chicks inevitably
starve.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.
Feeding
The Cattle Egret feeds on a wide range of prey, particularly insects,
especially grasshoppers, crickets, flies, and moths, as well as spiders,
frogs, and earthworms.In a rare instance they have been observed
foraging along the branches of a Banyan tree for ripe figs.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; in Africa, Cattle Egrets selectively foraged behind Plains
Zebras, Waterbuck, Blue Wildebeest and Cape Buffalo.Dominant birds feed
nearest to the host, and obtain more food.
The Cattle Egret may also show versatility in its diet. On islands
with seabird colonies, it will prey on the eggs and chicks of terns and
other seabirds.During migration it has also been reported to eat
exhausted migrating landbirds. Birds of the Seychelles race also indulge
in some kleptoparasitism, chasing the chicks of Sooty Terns and forcing
them to disgorge food. |
