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GREEN SCENE: Look (but not too closely) at Port Moody’s herons

Many people who stroll along the Shoreline Park trails in Port Moody have been delighted to observe the growing heronry this spring.
heron
The bright orange bill of this heron in its nest indicates egg laying is not yet completed.

Many people who stroll along the Shoreline Park trails in Port Moody have been delighted to observe the growing heronry this spring.

This colony, established only last year, attracted additional pairs of great blue herons this spring and now has seven nests under construction.

These herons are a unique subspecies that, unlike great blue herons in the rest of Canada, do not migrate south each winter. Fewer than 5,000 individuals of this subspecies of herons inhabit coastal areas of British Columbia. Because of their decreasing population, they are considered to be a species at risk. At just over a metre in height, great blue herons are the largest wading bird in North America.

Great blue herons seek out safe nesting sites in tall trees close to areas where they forage for food in shallow water. These herons mostly nest in groups, a strategy that is thought to provide some protection from predators such as eagles, crows and raccoons, which can raid their nests.

In the Lower Mainland, many herons nest in a few large colonies of a hundred or more nests. One such well-known heronry is in Stanley Park. Until 2012, another large heronry was located at the mouth of the Coquitlam River in Port Coquitlam. This heronry was abandoned that spring due to what was speculated to be ongoing construction/deconstruction noise from the nearby Port Mann Bridge. About half of these herons appear to have joined an existing heronry at Deer Lake in Burnaby while the fate of the remaining herons is uncertain. It is surmised the small heronry in Port Moody, which had three or four nests in 2015, may be comprised of some herons from the Coquitlam River group.

While most heronries are vulnerable to disturbance, especially early in the nesting season, the heronry in Stanley Park is situated in an area that receives considerable human traffic beneath the trees. Similarly, the small heronry in Port Moody is close to walking and cycling trails, so these herons also appear to have become accustomed to people on the trails. The city of Port Moody has installed a protective barrier to prevent people from leaving the trails as such an unusual activity could cause the herons to abandon their nests.

Initially, whistles from trains along the nearby tracks were also causing the herons to flush from their nests but, thankfully, the herons appear to be adapting. It is an offence under the BC Wildlife Act to disturb herons on their nests or to damage their nests at any time of the year.

Herons form new pair bonds each spring but will often reuse existing nests, which will require some repair after winter storms. During the breeding season, adult great blue herons develop elegant plumage along their necks and breasts in addition to their white head with a dark eyebrow plus dark epaulets on their shoulders. Their bills turn a bright orange to indicate their breeding status. This colouration quickly fades once eggs are laid.

It’s been wonderful to watch the herons build their twig nests in the Shoreline Park. The male brings a twig, typically stripped from a nearby tree, and presents it to its mate, which then decides where to place it. It should take about three days to construct a nest.

Herons typically lay about four eggs at intervals of two days. Because incubation starts when the first egg is laid, the eggs will hatch sequentially.

Thus, in a year when the weather is cold and food is scarce, only the oldest is likely to survive while, in a warm spring with abundant food, the younger nestlings may stand a change of fledging from the nest. In B.C., great blue herons are able to typically raise only one to two juveniles successfully.

Herons incubate their eggs for 28 days, with both males and females taking turns. In the first three weeks, nestling are unable to maintain their body temperature, so one parent must always stay on the nest to keep them warm.

Biologists estimate about two thirds of the food consumed by nestlings is used simply to keep them warm. Thus, a cold spring poses considerable challenges for their survival. By three weeks, the growing appetites of the nestlings require both parents to forage for food. Herons, which typically catch small fish such as sculpin and perch on an ebbing tide, will forage at sites up to 10 km from their nests, although it is advantageous to have an ample food supply closer to their nests.

Juvenile herons fledge from their nests at about two months of age and will quickly disperse. Once they leave the nests, their parents no longer feed them.

Without a doubt, the small colony in the Shoreline Park will continue to delight wildlife watchers over the next three months. It’s a great opportunity to observe a species at risk as they follow their eons-old survival strategies — but please remember to stay on the trails and do not disturb the herons during this critical time.

--Elaine Golds is a Port Moody environmentalist who is president and conservation chair of the Burke Mountain Naturalists, and member of the boards of the Colony Farm Park Association and the Port Moody Ecological Society.