Ian’s Bird of the Week – Cattle Egret by Ian Montgomery
At a time when wildlife populations are generally under pressure, here is a success story about a species of bird, the Cattle Egret, that has undergone a spectacular world-wide expansion in range over the past century of or so.
In the 19th century, the Cattle Egret occurred only in tropical and subtropical Africa, southwestern Europe (the nominate race, Ardea ibis ibis) and in southern and southeastern Asia (the distinctive race Ardea ibis coromandus). Now, it breeds in every continent except Antarctica, though it turns up as a vagrant on sub-antarctic islands such as South Georgia and the South Orkney Island. Originally adapted to feeding with large herbivores, its expansion has followed the of spread humans with their livestock.
The expansion started in southern Africa with breeding first recorded in Cape Province in 1908. At about the same time, vagrants started crossing the Atlantic to eastern South America, where it probably became established in the 1930s but breeding was not proven until 1950 in Surinam and British Guiana. Some birds were reported in Florida in the 1940s and breeding was recorded in 1953. Since then, the species has spread all over South and Central America, much of the United States into Canada and has simultaneously expanded its range in southern Europe and the Middle East.
Concurrently, the Asian race was extending its range southeastwards and arrived in the Northern Territory in the 1940s. Cattle Egrets were first record in Victoria in 1949, southwestern Western Australia in 1959, South Australia in 1964, Tasmania in 1965 and started breeding in Queensland in 1963, the same year in which they were first recorded in New Zealand. Now, it is an abundant breeding bird in the warmer parts of Australia and mainly a winter and spring visitor to southern Australia, Tasmania and New Zealand.
In non-breeding plumage, the feathers are almost entirely white (first photo, bird in flight) apart from traces of buff on the crown and looks like a dumpy version of the Intermediate Egret. When breeding the Asian/Australian race has extensive gold on the head, back and breast (second photo) and looks quite different from the much paler eastern race (third photo). The bird in the latter photo is perhaps atypically pale for an eastern bird, but it has the reddish bill, legs and iris that are the courtship colours of both races.
The fourth photo shows several Cattle Egrets standing guard in a proprietary manner around some young Brahmins at the Orient Wetland north of Townsville last Friday. Although they are very gregarious, the dominant birds exclude other birds from the favoured feeding spots just behind grazing animals. They feed mainly on grasshopper and other invertebrates disturbed by herbivores but are flexible and will eat a wide variety of other food including young birds. So, the global expansion has a dark side and I recently read an article, thank you Jeri, expressing concern about predation by Cattle Egrets on the nesting colonies of the Red-winged Blackbird in California (http://tricolor.ice.ucdavis.edu/ ).
Meanwhile back at the website, following last week’s release of the revised home page, I’ve been working on redesigning the family pages and species galleries to make them neater and easier to use. It will take time before the revisions get generally applied but you might like to check out the Crane family thumbnails(http://www.birdway.com.au/gruidae/index.htm ), colour-coded by region, and the Brolga gallery with larger images (http://www.birdway.com.au/gruidae/brolga/index.htm ). I’ve also increased the size of the photos in this week’s bird of the week. This will mean that I’ll probably often exceed the intended limit of 200KB for the weekly posting. Let me know if this is going to be a problem, but I suppose most of us now have broadband internet.
The Cattle Egret is now, according to the I.O.C., divided into 2 species. The Eastern Cattle Egret (Bubulcus coromandus) and the Western Cattle Egret (Bubulcus ibis). The Eastern breeds in Asia and Australasia, and the western nominate form occupies the rest of the species’s range. Here in the United States, we have the Western Cattle Egret. Those of us who live here in Florida see them all the time, just like in Ian’s forth picture. You will see one or more per cattle. They love to stand right by them and look for bugs or whatever as the cows pull up the grass to eat. They seem to get along and the cattle don’t seem to mind them standing there, almost in their face sometimes. Thanks, Ian, for more great photos and information.
Now behold, I Myself do establish My covenant with you, and with your descendants after you; and with every living creature that is with you, the birds, the cattle, and every beast of the earth with you; of all that comes out of the ark, even every beast of the earth. (Genesis 9:9-10 NASB)