It could be due to my local boyhood pride, but few North American birds continually capture my attention like the Great White Heron. When I watch this imposing hunter make its presence at the shallows of Florida Bay, and take its rightful place at the head of the massive flocks of waders and shorebirds, its hierarchy at the very top of the pecking order seems indisputable.
When John James Audubon wrote about it, soon after discovering the bird off Indian Key in April of 1832, he introduced it to the world as the “largest species of the Heron tribe” in North America. He immediately understood that the science community would find this all-white heron startling, and cautioned that “our endeavours to discover the natural arrangement of things cannot be uniformly successful.” Ever since, ornithologists have argued and disagreed about the provenance and status of this saltwater wader.
Whether the Great White Heron (currently Ardea herodias) is a species, a subspecies or simply a color morph is an age-old argument that exemplifies the problems inherent to taxonomic categorization. It might even be argued that all manifestations of the “Great Ardea Heron” in North America are part of a single widespread species that includes the Great Blue Heron, the Cocoi Heron in South America and the Grey Heron in Europe.
What should not be argued is that a unique and significant variation of the Ardea heron – coined occidentalis – limits its North American presence almost entirely to Florida Bay and the Keys. The case of the Great White Heron isn’t simply that of a white plumaged Great Blue as it’s sometimes suggested. Aside from its overall color, the Great White exhibits a number of structural differences that make its careful study rewarding.
During years of observing these magnificent birds, I have carefully drafted portraits of distinct individuals throughout the region to compare them for bill size and facial bare parts. I’ve documented dozens of Great White and so-called “intermediate” Würdemann’s Herons, and have noticed some interesting tendencies. Aside from the apparently larger bills, South Florida Great Whites show a greater amount of bare skin around the bill and loral region, and particularly surrounding the “mouth” [a1], compared to other A. herodias.
The “straight” culmen of the Great Blue is often mentioned, and by proxy this is assumed of the Great White Heron. “Northern” Great Blues often show a mostly-straight culmen [c5] with a very subtle “flattened” dip halfway to the down-curved tip, yet the occidentalis herons consistently show a slight and relatively continuous outward curvature to the culmen [a5]. After studying a small sample of Great White skulls from Florida Bay with those of mainland Great Blues, I have found similar differences.
Perhaps the feature that gives Great White Herons that particular commanding expression is the “grimace” formed by a greater amount of bare skin around the corner of the mouth, fully exposing the upper edge of the lower mandible at its base [a1]. This exposure is weak or absent in “Ward’s” herons, and limited to the upper mandible in A. h. herodias. Additionally, these exposed “lips” tend to be pale in Great Whites only, and may be bright yellow during breeding season.
These subtle distinctions, however, become blurred when the “Würdemann’s” Heron is taken into consideration. I have found that intermediate herons often lack the bare lower “lip” of Great Whites despite the pale heads of most individuals. Does this tell us anything of importance about the relationship between this taxonomic form and its congeners? Due to the limited scope of my study, I only intend to pose simple questions to further the discussion.
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The myth of a classic “Würdemann’s” with a Great White head and a Great Blue body is shattered after spending plenty of time surveying Florida Bay for waders. It would seem that any dark Ardea heron breeding in Florida Bay and the Keys is some kind of an “intermediate”. Their plumage varies from birds with pale heads and necks to those indistinguishable from a typical dark Ardea herodias.
I do not propose that my observations contribute something valuable to the argument of Great White Heron classification – they are perhaps too mired in the zone of art – but I do propose that we should pay closer attention to this unique taxon, for we still have much to learn of it.
Recent research (Zachow 1983, McGuire 2002) suggests significant structural and genetic differences between the overall larger occidentalis herons and the peninsular Great Blues. “Würdemann’s” Herons have been shown to have closer genetic and structural affinities to Great Whites (McGuire). There is no evidence of substantial genetic flow between Ardea herodias – white, blue or intermediate – breeding in Florida Bay or the Keys, and birds breeding in the Florida mainland.
This article was originally published in the Fall of 2010 issue of the Tropical Audubon Society print publication.