Great blue herons are found in High Park along with night herons and giant white egrets. They are one of the largest and most majestic of the Parks visitors. They are unobtrusive and incredibly patient hunters. Their presence in the Park indicates that the water in Grenadier Pond sustains fish, its main food, and provides sufficient habitat of privacy and shallow shorelines.
They arrive in the area in early April. Most local birds winter south of Ontario. However some birds have begun to stay in areas of southern Ontario with open water. Great blue herons always live near sources of water, including rivers, lake edges, marshes, and swamps. They usually build their nests, comprised of a large platform of sticks, lined with pine needles, moss, reeds, dry grass, or twigs, in tall dead trees or bushes that stand near water, or occasionally, on the ground. They usually breed in groups, and during the day they will sleep with flocks of over 100 other herons. Great blue herons are also extremely territorial and will aggressively defend their nests. They will sometimes nest as a lone pair.
Great blue herons are the largest and the most well-known and most widespread heron in North America. They stand approximately 60 cm tall and are 97 to 137 cm long. They weigh 2.1 to 2.5 kg. They have long, rounded wings, long bills that taper to a point at the end, and short tails. They also have very long necks and legs. The bills are a yellowish color and their long legs are green. Great blue herons have gray upper bodies, and their necks are streaked with white, black and rust-brown. They have grey feathers on the back of their necks with chestnut colored feathers on their thighs. The males have a puffy plume of feathers behind their heads and also tend to be slightly larger than females.
Great blue herons generally have one mate per breeding season. They typically breed from April to May. Females lay between 2 and 7 pale blue eggs. Both parents take turns sitting on the nest to keep the eggs warm until they hatch. The eggs hatch after 26 to 30 days of incubation. Both parents care for and feed the chicks, by regurgitation of food, until they are ready to leave the nest. The largest chicks receive the most food. After living in the nest for about 2 months, the chicks are old enough to leave the nest and survive on their own. Herons become sexually mature when they are about 22 months of age.
The oldest wild great blue heron was said to be 23 years old, but most do not live so long. The average lifespan for a great blue heron is around 15 years. As with most animals, they are most vulnerable when they are young. More than half of the great blue herons born in one year will die before they are a year old. Crows have been reported eating heron eggs. Raccoons, and red-tailed hawks, prey on the young birds and sometimes even the adults. Birds will abandon a colony where they have been living after a predator has killed an adult or chick in the area.
Great blue herons are relatively quiet compared to other related species. They release a soft "kraak" when they are disturbed in flight. Other heron calls include a "fraunk" when they are disturbed near their nests which usually lasts about 20 seconds, and an "ar" when they are greeting other members of their species. These herons are known to have up to 7 different calls. They also snap their bills together and use complicated body movements in courtship displays.
Great blue herons fish in both the night and the day, with most of their activity occurring around dawn and dusk. They are solitary predators, preferring to hunt alone. Herons use their long legs to wade in shallow water and their sharp "spear like" bills to catch their food. It will hunt by standing still, with great patience, in areas where fish are swimming about and when one comes within its reach, it stabs the prey with quick lunge of the bill catching the fish sideways in its bill. If the fish is small enough it will toss the fish in the air and swallow it head first. The heron may also stalk its prey by moving along a shoreline watching for fish. Their long legs allow them to fish a niche that is not available to other herons. Great blue herons' diet consists of mainly fish, particularly pumpkin seed in High Park, but also includes frogs, salamanders, lizards, snakes, birds, small mammals, shrimps, crabs, crayfish , dragonflies, grasshoppers, and many other aquatic insects. Herons locate their food by sight and usually swallow it whole. Herons have been known to choke on prey that is too large. Great blue herons control fish and insect populations in many different habitats. They are a delight to watch and they, along with the species that they eat, are important indicator of the health of the Grenadier Pond ecosystem.
They can co exist with human habitation as long as suitable nesting woods and wetland feeding sites are available. Grenadier Pond, the lower duck pond and other lakeshore parks provide the necessary habitat in the Toronto area. Human interference with the heron primarily involves destruction of habitat through farming and urban and park development into marshy areas. Many herons are also killed each year due to collisions with utility wires. Great blue herons are protected by the United States Migratory Bird Treaty Act.
Great blue herons have up to 7 known subspecies. One interesting subspecies is the great white heron, with mostly white plumage, that lives mainly in Florida and the Caribbean.
Sources consulted and utilized Naumann, R. 2002. "Ardea herodias" (On-line), Animal Diversity Web. Accessed October 05, 2009 Atlas of the Breeding Bird of Ontario Cornell Lab of Ornithology Environment Canada/Canadian Wildlife Service Bulletin 135, US National Museum, North American Marsh Birds Wikipedia
Compiled by Ken Sharratt