As the days lengthen and warm, marine fish move into shallow water. Their arrival is important for great blue herons which gather at the tideline. Nowhere is this more evident than on Roberts Bank where hundreds of herons congregate through spring and early summer, feeding in the intertidal area and nesting on the adjacent wooded bluff on Tsawwassen First Nation land.
Extraordinary as it may seem, these long-legged, long-necked birds build flimsy stick nests, high up in alder, maple or Douglas-fir trees. The Tsawwassen colony has over 300 heron pairs, with often three or more nests in a tree, and is the largest heronry on the Canadian west coast.
In winter, the herons disperse into farmland and marshes around the Fraser delta, where they catch voles and other small mammals. However, once starry flounder and shiner perch begin to arrive in inshore waters, the herons move to a diet of fish; later in the summer, they will also eat frogs and snakes. Endemic to the Pacific northwest, the local subspecies of great blue heron has grey, black, and white feathers and plumes. In March, their bills turn bright yellow-orange, indicating their breeding readiness. Pair bonds are formed and the noisy business of nest building begins.
Prior to 1955, the herons nested in woodland near Tsawwassen’s current town centre, but forest clearance forced them to repeatedly move. By 1973, the colony had settled in Point Roberts, WA, close to the Canadian border, where it remained for twenty years, growing to nearly 500 pairs. Tree clearance adjacent to the heronry and increasing predation by juvenile bald eagles, the population of which was increasing, caused nesting failure in 2003. Nests and eggs were suddenly abandoned, and no young were raised.
The following spring, some of the herons moved a few kilometres north to their current location, and within a couple of years they were all settled in. Rather curiously, they settled in trees around one that was already occupied by a mature pair of bald eagles. Could the herons somehow know that the territorial behavior of adult eagles would keep unruly juveniles away? A study has since shown that great blue herons nesting within 200m of an eagle nest have comparatively greater reproductive success. Heron species survive successfully all around the world; their innate wisdom must be greater than we appreciate!
When observing the herons, please respect their need for quiet and calm surroundings, and the privacy of the Tsawwassen First Nation property.
Anne Murray’s books on Delta’s natural and ecological history, A Nature Guide to Boundary Bay and Tracing Our Past, a Heritage Guide to Boundary Bay, are available in local stores or from www.natureguidesbc.com. She blogs at www.natureguidesbc.wordpress.com
