Great Blue Heron
Ardea herodiasGreat Blue Herons are found all across North America, however, local Pacific Northwest herons are non-migratory and are considered to be genetically distinct from all other populations.
Standing about 4 feet (1.2 meters) tall with a wingspan of about six feet (1.8 meters), they are one of B.C.'s tallest native birds. However, they weigh only about 5-6 pounds (2.5 Kg). Adults have a bluish grey body with white crown and face but a black fedora on its head. Plumy feathers called aigrettes on their chest and back and a black patch on each shoulder complete their stately outfit.
Herons belong to the order Ciconiiforme, which are wading birds who have long legs, neck and bills, broad rounded wings and short tail. Members of the Ardeidaeis family share characteristics with other herons and bitterns: straight bills, slow flight and tucked neck. They can be told apart from similar-looking but not related crane order because a special vertebra in the front of their neck (looks like an adams apple) allows them to tuck their neck in an S-shape in flight and move their head head quickly forward while feeding. Cranes fly with their neck outstretched.
Herons are solitary birds who feed by standing still in shallow water or long grass. They watch for movement of prey, then slowly lower their heads, to within striking distance. They are patient and wait for the right time, then they rapidly strike and imperil prey on their sharp beak. Fish, frogs and voles are flipped so they are swallowed head first. They have very good vision, particularly in good low light conditions. Sometimes heron will catch a fish that are too large for them to eat and will simply leave it behind for other predators and scavengers such as mink or eagles to eat.
Because they eat the entire body of their prey, bones that are too large to be digested and feathers or fur that are not digested are regurgitated in the form of a casting.
These birds nest in colonies called heronries where as many as 500 active nests in one heronry has been counted. Most colonies are much smaller with about 20-50 nests. A few birds will nest individually as well.
Males arrive early in the spring (about March)and choose a nest. The females arrive later and are selected by the males and nest repair begins. One courtship study found that 14 physical behaviors and 7 to 9 vocalizations were specifially connected with pair bonding. Males choose a new mate each spring.
Each pair lays about 4 pale blue duck-sized eggs which the adults take turns incubating for about 28 days. Once the young hatch, the search for food begins and intensifies as the growing young need more food each day.
Young grow quickly and within a few weeks are already testing their wings. From the time they are laid to the time they learn to fly, only about 50 percent will survive due to competition for food and predation by red-tailed hawks, ravens, bald eagles, and raccoons. In about 6 weeks the young are as large as the adults.
During the winter, males stake out prime territories on intertidal beaches, while females and young look for voles in less productive fields. Young are not as good at catching food as adults (about 50 percent of fishing ability) and so only one quarter will survive to one year of age. Great Blue herons are mature at two years of age but may not breed until their third year.
Colonies are noisy with adults and young vocalizing constantly and the trees and ground below the nests are covered with a solid layer of fishy smelling heron frosting (droppings). Colonies are usually located near protected beaches, wetlands and fields so parents can find food nearby and travel back and forth carrying a full crop of food. Rapidly growing young are fed a diet high in fats and protein. Fish called Shiner Perch who spawn in eelgrass beds are caught by wading adults, eels, fresh water fish, garter snakes and frogs are also caught. A small mouse-like creature called a vole is another food high in protein. Young are fed regurgitated prey species.
Because of their dependence of a variety of habitats (forest, field and wetlands), they are known as keystone species or bio-indicators because any major change in their environment will greatly affect their population. If exposed to toxins such as DDT in their environment, their eggs show a high concentration of the toxin.
In addition, they are very sensitive to human disturbance during nesting and will abandon their nests, eggs and young if disturbed. To protect themselves, young will regurgitate food.
One particular heronry has been of interest to local individuals and companies. At its peak in 1995, active nests numbered 500. (more than 3500 birds). However, in the last 20 years, there has been a general decline in the Pacific Northwest population of 5.7 percent per year and they have been declared a vulnerable species. Their largest threat is land development and human presence. The Point Roberts Heron Preservation Society has been created to help educate people, do lobbying and purchase the property where the heronry exists as well as some of the land around it. If you would like more information or would like to help, please contact them:
Point Roberts Heron Preservation Society
Point Roberts, Wa.
by Donna Hill B.Sc. B.Ed. 1998
Many thanks to Ann Eissinger, heron expert, for sharing this information during her presentation. Contact her if you have questions about the biology of local BC herons.
Here is a good book on the topic: Great Blue Heron by Robert W. Butler 1997 UBC Press (can be ordered by contacting UBC Press
If your group wants to learn more about herons and other birds or wetland species, and would like a guest speaker to visit your class or group,
go to Birding in the Field or go to Wetlands and contact us to book a program date.