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.
South Coast BC Distribution. Main breeding colonies (green) and potential occurrence range (red-dotted line)
Habitat (especially during breeding season) ranges from 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.
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.
For colony specific details on Pacific Great Blue Heron breeding and rearing chronology contact the Great Blue Heron Working Group.