In late April 2012, Roy Halpin found and photographed an entirely buff-colored Cattle Egret in Saint Augustine, Florida. This is a particularly interesting bird because it provides an opportunity to consider the unusual nature of Cattle Egret coloration, as well as the identification of Cattle Egret subspecies.
Coloration in Cattle Egrets
To understand this bird’s coloration, it’s important to understand the unusual source of the buff color in Cattle Egrets. Evidence suggests that the buff color of Cattle Egrets is essentially a stain, coming from pigmented oil from specialized powder-down feathers (Delhey et al, 2007). When a Cattle Egret molts in late summer the new feathers are all-white, and they slowly turn buff in winter and spring without molting.
I don’t think the Saint Augustine bird is stained by some man-made chemical because the color of the head and back plumes looks typical for Cattle Egret, and because the color is so smooth and uniform throughout, including even the underwing coverts. I will speculate that this bird is over-producing the oils from powder-down, and coloring the whole plumage. The darker color on the wing coverts could be the result of the pigmented oil interacting with differently-textured feathers there.
Obviously there is a lot more to learn about Cattle Egrets and the details of their coloration. If this individual can be refound and photographed at different seasons or in subsequent years that might offer some clues, and looking for similar anomalies in other Cattle Egrets could add important clues. I can’t help but wonder if the dark Cattle Egrets discussed in a previous post here are related in some way to anomalies of powder-down coloration.
First, this is clearly a Cattle Egret, despite the unusual coloration. There is no other small egret that could be confused with it, and no hybrid combination that would account for the color. It is simply a Cattle Egret with a lot of buff color.
Identifying the subspecies is another matter. The Asian subspecies of Cattle Egret is distinguished from the African/American subspecies primarily by its more extensive (and darker) buff color on the neck and body. This subspecies has been recommended for full-species status, and has occurred in the western Aleutians. It is a potential vagrant anywhere in North America, and a potential species and therefore would be of great interest to birders here.
Briefly, the Asian subspecies B. i. coromandus differs from the common American/African subspecies B. i. ibis in the following ways:
- buff color is more extensive, covering the entire neck, but leaving the face and most of the body white
- the buff color is distinctly darker, more cinnamon-orange, rather than the pale frosty pinkish-buff of ibis
- overall size averages slightly larger
- bill averages slightly heavier and longer
- legs average slightly longer
Differences in size and proportions are slight and overlapping, making the extent and shade of the buff color the only really useful features to distinguish these two subspecies. In both respects the Saint Augustine bird does not fit the Asian subspecies.
In the 1980s I saw an extensively buff-colored Cattle Egret in southern Florida, which was the model for the illustration on page 64 of the Sibley Guide to Birds. Recently I was thinking about that sighting, and wondering if it could have been a vagrant from Asia. I will never know for sure, but this Saint Augustine bird shows that American Cattle Egrets can be buff-colored all over, and offers a much more likely explanation. Still, any Cattle Egret with extensive buff color should be checked for the possibility of the Asian subspecies.
Delhey, K., Peters, A. & Kampenaers, B., 2007. Cosmetic Coloration in Birds: Occurrence, Function, and Evolution. The American Naturalist, 169, pp.S145–S158.
Photos by Roy Halpin, originally posted at Digiscoper Magazine here: http://digiscopermagazine.com/?p=2478
Thanks to Satoko Lincoln for bringing this to my attention, and to Roy Halpin for allowing use of his photos.