Heron Information and Conversation Knowledge
Information
Great Blue Heron (Ardea herodius) is the largest and most widely distributed heron in Canada. During the breeding and post-breeding seasons it ventures as far north as Newfoundland and Prince William Sound in Alaska, and as far south as Mexico and the West Indies. Herons leave most of Canada for the winter, the exception being the British Columbia coast, where herons reside all year round. They also winter across the United States and south to Panama, Colombia, and Venezuela.
Two subspecies occur in BC : the coastal fannini ssp and the interior herodias ssp.
Range
Elevation: 0-1100 m. The fannini subspecies of Great Blue Heron is found throughout the Coast Region. While foraging and breeding sites are quite dispersed, this subspecies is more common on the South Coast especially in association with low elevation lakes, wetlands, sloughs and estuaries. The major nesting colonies (“heronries”) on the South Coast include: Tsawwassen, Bowen Island, Deer Lake, UBC (main campus) and West Vancouver. Many of these locations support >100 nesting pairs. Other heronries occur on the Southern Gulf Islands and southeast Vancouver Island. A major heronry located at the confluence of the Coquitlam and Fraser Rivers adjacent to Colony Farm Regional Park became abandoned around 2012. Although some nesting may still be occurring there. It is estimated that approximately 4-5000 breeding birds make up the coastal subspecies population in BC, with some heronries like Tsawwassen supporting at least 10% of that population.
Distinctive Features
On the ground, adult specimens stand over 1 metre in height. the head is white with a black stripe on each side extending back from the yellow eyes to slender black plumes. The back is greyish blue and the breast is white streaked with black. In flight, the neck is doubled back and the head rests against the shoulders. Herons in their first year have grey crowns and grey wing flecked with brown.
Habitat
Habitat (especially during breeding season) includes riparian areas, estuaries, lakes and lowland rivers and streams. Foraging habitat includes: Eel grass beds, mudflats, agricultural fields and old-field (mainly short-grass or mowed), wharves, beaches, irrigation ditches, urban lakes, streams, drainage ditches and backyard ponds. During non-breeding periods birds roost high up in mature trees in close proximity to foraging sites. Heronries are typically found within 10 km of foraging habitats. Though generally associated with stands of trees well away from noise, light and human disturbance, some heronries (e.g. Stanley Park), have become established in dense urban areas. Canopy closure is a factor for heronries, typically being >80%, though birds have been known to use stands with more open canopies. Heronries can be over 350 nests and sites are reused in successive years. Small nesting colonies are more common on the Sunshine Coast and on Vancouver Island. Nests are located at 4-70 m above ground and consist of large stick platforms, < 1 m diameter. Nests are constructed on the horizontal branches of mature trees, often Black Cottonwood, Bigleaf Maple or conifers. Nests are lined with twigs; bark strips, coniferous boughs and rushes. Both the nest and the ground beneath are often covered in droppings, discarded food, and occasionally dead chicks.
Diet
Primarily a fish eater (pisciverous), this subspecies also exploits a range of amphibians including invasive species such as Green Frog and American Bullfrog. Small mammals such as Townsend’s Vole, mice and shrews are stalked in meadows and agricultural fields and may form an important component of the diet in winter in certain areas.