Great blue herons (Ardea herodias) are common in much of North and Central America and are the largest heron species across their range (although white-bellied herons from India, Burma, and Bhutan, and the aptly named goliath herons from Asian and Africa are larger).  Great blue herons can be as tall my grandmother (around four and a half feet tall) and have a wingspan of between six and seven feet (significantly exceeding nana's).
 
Although the diet of great blue herons is composed primarily of small fish, I have confirmed Collazzo’s (1979) claim that voles form a substantial part of their diet (gross).  They migrate only when and from areas in which their fishing waters freeze.  Herons are seasonally monogamous (Butler, 1992) but, like humans, often select new mates each spring.  Young herons grow to almost 90% of their adult weight within 45 days of birth (Quinney, 1982) thanks to the generous regurgitation of their parents, and begin to fly at about two months of age.
 
Groups of herons nesting near each other are called heronries. Heronries can include as many as 500 nests (Short & Cooper, 1985), although many of the pictures in this month’s Special Project, from the Lee Metcalf National Wildlife Refuge are from a small group of perhaps 15 nesting pairs.
 
While often exhibiting laser-like focus on the movements of small fish in the creek below them, great blue herons have to keep a wary eye upward for various raptor species especially bald eagles but also including golden eagles, red-tailed hawks, and great horned owls.  Keeping the other eye down is also a good idea as both alligators and crocodiles attack inattentive herons (Simpson, 1984).  Avian and amphibian predators are not the only concern of herons, however, as the Audubon Society (2016, paragraph 1) noted, a great blue heron in North America was “Formerly often shot, simply because it made a conspicuous and easy target.”  So proud to be human right now.     

References

National Audobon Society. (2016). Great blue heron. Retrieved from http://www.audubon.org/field-guide/bird/great-blue-heron

Collazo, J. A. (1979). Breeding biology and food habits of the Great Blue Heron at Heyburn State Park, Benewah County, Idaho. Master's Thesis. Univ. Idaho, Moscow.

Quinney, T. E. (1982). Growth, diet, and mortality of nestling Great Blue Herons. Wilson Bulletin, 94, 571-577.

Short, H. L., & Cooper, R. J. (1985). Habitat suitability index models Great blue heron. Biological report 82(10.99). Washington, DC:
Western Energy and Land Use Team, Division of Biological Services, Research and Development, Fish and Wildlife Service.

Simpson, K. (1984). Factors affecting reproduction in Great Blue Herons (Ardea herodias). Master's Thesis. Univ. Brit. Col. Vancouver.

Butler R. W. (1992). The Great Blue Heron. In Birds of North America, No. 25. Available from http://bna.birds.cornell.edu/bna

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