Friday, September 16, 2016

Great Egret at CSU Stanislaus

Since a few days ago I mentioned the snowy egret (Egretta thula) that lives on the campus of CSU Stanislaus, I thought I'd go ahead and add a post about a pair of great egrets (Egretta alba) which share the same ponds.

But first : how to distinguish between the two species of white egrets commonly seen in California.

I was lucky enough to get this shot of both species standing side by side for an excellent comparison.
Compare: size difference, feet color, bill color
The most obvious difference is their size; the great egret is, fittingly, significantly larger than the snowy egret.  However, as any birder will tell you, never judge a bird on size alone!  Perceived size, dependent on many variables, can be deceiving.  That is why it is valuable to learn field marks.
Great egret, with yellow bill and black feet
Noteworthy field marks for the snowy egret are its black bill, black legs and yellow feet.  Looking at just the feet and bill, the field marks are reversed for the great egret: yellow bill and black feet.  These features are an easy way to confirm an identification. 
While the lores (areas of skin between the bill and eye on either side of the head) of the snowy
egret turn red during peak breeding season, those of the great egret turn bright green. 
In September, this egret is still showing a hint of that green.
Great egrets have similar habits to those of the snowy egret.  The are associated with wetlands (including both fresh and saltwater), nest colonially, and prey mainly on fish, but also on marine invertebrates and small mammals, reptiles and amphibians.  Their preferred method of hunting is to stand still, waiting for an animal to swim by, then strike with their bill, spearing their prey.  Like the snowy egret, great egrets also grow beautiful white plumes during the breeding season, which were coveted by humans and led to a decline in the bird's population.
Great egret, in typical egret habitat: a wetland margin, surrounded by cattails (Typha sp.)

(Aside: Cattle egrets (Bubulcus ibis), though not treated at this time, are a third white egret found in California.  They are smaller than the great egret, with a shorter, stouter bill and generally stockier appearance.  Adult cattle egrets have a yellow bill and yellow to pinkish legs; juveniles have dark bills and legs.  Cattle egrets spend most of their time in grassy fields, often associated with livestock, and rarely are associated with wetlands, as are snowy and great egrets.  Cattle egrets are originally from Africa, and were introduced to North America in the 1950's.)

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