Friday, October 28, 2011

Cattle Egret

On recent trip to Squaw Creek NWR in Mound City Missouri I spotted these three cattle egrets cleaning their feathers and sunning themselves on a stump in the marsh. They were approximately 10 feet off the shoreline and very tolerant of human activity. I was able to photograph them from the car without disturbing them at all.

Cattle Egrets (Bubulcus ibis) are closely related to herons such as the Great blue Heron, Purple Heron and the Green Heron. Cattle egrets will be found in tropic, sub-tropic and temperate zones and are often associated with cattle, hence the name. They feed on the insects disturbed by the large hooved animals.This species also removes ticks and flies from cattle, but it can be a safety hazard at airfields, and has been implicated in the spread of tick-borne animal diseases. It is not uncommon to see huge flocks of over a hundred of these egrets in a pasture with cows. I saw such a flock several years ago when we visited Oklahoma.
They do nest in large colonies near bodies of water much like other herons and egrets do. Their nest is a platform of sticks. These birds as adults have few natural enemies, but the eggs and chicks are often preyed upon by raccoons, snakes, and other predators.

The Cattle Egret is a stocky heron with 35–38 inch wingspan;and weighs 9.5–18.1 ounces. 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 of the 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. The positioning of the egret's eyes allows for binocular vision during feeding, and physiological studies suggest that the species may be capable of nocturnal activity. This species gives a quiet, throaty "rick-rack" call at the breeding colony, but is otherwise largely silent.

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. They were orginally from Southern Spain and Portugal. 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 kept spreading 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. Its global population estimated to be 3.8–6.7 million individuals.