GOLDS: The herons of Colony Farm, alone and together
March kicks off a series of nature walks at Coquitlam’s Colony Farm Regional Park with a focus on its birdlife.
This park attracts an impressive diversity of birds, including a number that are rarely found in the Lower Mainland. One reason for this is its open meadows, termed “old-field habitat” by biologists. These meadows, in combination with some shallow water channels, ponds and riparian forests, attract approximately 200 species of birds to Colony Farm Park.
The old field habitat, somewhat reminiscent of the prairies and interspersed with shrubs, represents a type of habitat of which little is protected within Vancouver area parks.
Prior to European settlement in the region, the land at the edge of the Fraser River delta would have been mainly old field habitat merging into marsh at the water’s edge. There is evidence these tall grass meadows were, in part, created by First Nations, which set infrequent fires to promote the growth of berry-producing shrubs, on which they relied for food. Although herons are more typically observed predating on fish or salamanders in shallow water, during the winter, when water freezes, the herons switch to old field habitat to search for food.
Throughout the winter months, volunteers with the Colony Farm Park Association monitor the activity of herons in the fields at the park. Knowing which fields are used by the herons helps park staff to make decisions about field management.
The main source of food for herons in the tall grass meadows is deer mice, voles and frogs, which are also predated upon by owls, hawks and harriers. Hunting is typically a solitary activity, with each heron carefully guarding its own territory.
But by early March, volunteers begin to notice a distinct change in the behaviour of the herons. As the nesting season approaches, these birds abandon their solitary habits and begin to congregate and, eventually, a large group of herons forms.
Unlike cranes, which dance and bow to one another, the behaviour of the herons is more like awkward teenagers at their first high school dance. The herons simply roost together in a large group for much of the day and there appears to be little evidence of any interaction between them. Finally, the herons move, as a group, toward their nesting site, which is close to Colony Farm Park in a large cottonwood forest at the mouth of the Coquitlam River. Soon after that, nest-building activity begins in earnest and herons can be observed carrying relatively large twigs to their nest site.
The species of great blue herons in this part of B.C. is a unique subspecies that does not undertake long migrations south every winter. Because their numbers are limited, they are considered to be a species at risk in British Columbia.
In the Lower Mainland, these herons tend to nest in large colonies, typically in cottonwood forests close to the water’s edge. Because urban development and industrial activities have resulted in the loss of many forested areas along the Fraser River, there are few remaining areas capable of supporting a large heronry. Often, herons have to compete with bald eagles and red-tailed hawks for suitable nesting sites, which sometimes leads to eagles predating upon the occasional heron chick.
The area where the herons nest at the mouth of the Coquitlam River has been protected as a Wildlife Management Area since 1995. When it was first protected, it supported a colony of herons with about 50 nests. Since then, it has grown in size and is now estimated to consist of approximately 110 nests.
During the time that the new Port Mann Bridge has been under construction, biologists have been hired to monitor this heronry to ensure construction activities do not disturb the herons on their nest site. This is resulted in valuable information being compiled about the site and annual success of each nesting season.
TAKE A WALK IN THE PARK
On Sunday, March 17 and Saturday, March 23, volunteers from the Colony Farm Park Association and Burke Mountain Naturalists will lead public nature walks at Colony Farm Regional Park with a focus on the activities of the herons. These walks, which will leave from the parking lot at the end of Colony Farm Road in Coquitlam, will start at 10 a.m. and last for approximately two hours. The walks are free of charge and suitable for all ages; registration is not required. Later in the season, on International Migratory Bird Day on May 11, another family nature walk will be offered at Colony Farm Park. For additional information and updates, visit www.bmn.bc.ca.