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The Stanley Park Heronry Journal
Introduction
On a warm, clear evening in early July, I'm standing under a broadleaf maple tree looking almost straight up through binoculars, examining a great blue heron and trying to determine if it's a chick or an adult. Due to the bird's position, I can't see the crest on its head, its breast, or wings. The bird is leaning toward me; all I see are the legs, the face, and the body surrounding the face. Then I realize the bird is looking straight at me! I lower the binoculars and look up, and its gaze is still on me. Through the binoculars, I inspect the yellow eyes, which appear to be staring intently under bushy, Groucho-like eyebrows. Fair enough, I think. I've spent so much time watching these birds, now it's their turn to inspect me.
Background
The great blue heron, Ardea herodias, is the largest heron in Canada. The herons in Stanley Park belong to a subspecies, Ardea herodias fannini; they are found along the coast and islands and are non-migratory. Great blue herons in British Columbia are protected under both federal and provincial laws, under the federal Migratory Birds Convention Act and Migratory Birds Regulations, and the provincial Wildlife Protection Act. It is an offense to alter or destroy their habitat, harass them with motor vehicles, boats or aircraft, to possess or injure birds or nests, or hunt them. Under federal legislation, the nests, eggs, young and adults are protected.
The heronry in Stanley Park is considered the oldest in the lower mainland. Records of herons nesting at Brockton Point start in 1921. The colony remained there for 50 years before relocating to the Stanley Park Zoo where it lasted another 30 years. 2001 was the first year they nested in the current location close to the Park Board office and tennis courts near English Bay.
Biology
An adult great blue heron stands approximately one meter high and has a wingspan of up to two meters; it weighs just over two kilograms. Males are slightly larger than females, and their bills one to two centimeters longer.
Herons begin courting in February; once the female has chosen from eligible males, they both begin nest construction (or renovation if they choose to occupy an existing nest). The nests can be up to a meter in diameter and they have a depression up to 10 cm deep.
Great blue herons lay clutches of three to five eggs, and the eggs are often laid over a period of days, with one to three days between laying. The incubation period is approximately 28 days, and again the timing is staggered, with intervals of a day or two between hatching. The greenish-blue eggshells are discarded outside the nest after hatching, probably to discourage predators, insects, and decomposition. The female broods during the night, while the male stays during the day. The nutritional requirement of a heron chick is great, as it will increase its mass approximately 40-fold in two months, from an initial weight of approximately 50 grams to 2 kilograms.
After about three weeks, when the chicks can maintain their body temperature, the parents leave them alone in the nest. The efforts of both parents are required to feed themselves and their growing chicks. For the most part, the chicks remain quietly in the nest until a parent returns with a meal. The returning parent will often pause on a nearby branch for five to ten minutes before making its way to the nest and regurgitating its catch of fish.
Chronology
March
My initial survey of heron nests was made March 16, on a cold Saturday afternoon. The leafless branches of the deciduous trees made spotting most nests easy, but without the help of other observers I might have missed the nests in the towering Douglas fir near the parking lot serving the tennis courts and Fish House Restaurant. It sheltered four nests, and by the end of the month a fifth nest was under construction. One friend, a seasoned birder, came with me to observe the herons on the last Saturday of the month; she had no trouble finding all the nests in the fir tree and even swore she saw a heron chick, which I did not see. The maple at the junction of Nelson Street and Lagoon Drive contained three nests. Another maple tree, near the south end of the large tennis court, housed four nests, and I observed a fifth under construction Easter Sunday evening as I walked off dinner with friends and family. The last site I confirmed was a single nest in a maple tree close to the parking lot at the Park Board office. This lone nest was easy to find and easy to monitor, and early in the season it was occupied most of the time.
April
In the second week of April, the switch to daylight savings time meant that I could monitor the birds more often than just once a week: the later sunsets gave me the opportunity to see the birds after getting home from work. I usually was able to see birds at all the nests, although sometimes I had to wait a while; despite their size, the herons proved very difficult to see from the ground. Eventually, though, the nesting bird would get up to stretch and reposition itself.
On occasion, two birds would be at the nest, sometimes flapping their wings and touching beaks. I observed birds making several visits to their nest with branches and twigs gathered from nearby cedar and fir trees.
I found the first two eggshells early in April - greenish blue, sturdy, not much larger than chicken eggs - on the ground under the Douglas fir. I saw my first chick two days later. Unfortunately, it was a carcass being eaten by a crow. I could not get within three meters, but could see through my binoculars the unmistakable beak and elongated neck.
As April progressed, I picked up clues about monitoring the birds. Looking at the ground, I found not only eggshells but also other signs of habitation, such as guano (bird droppings) under the trees, and guano-stained branches, moss and lichen.
The maple beside the Park Board parking lot seemed deserted for the last half of April. If not for the guano under the nest, I might have given up on it.
By the end of April, I was monitoring 14 nests, 13 of which were occupied.
May
May started off very exciting. Under the maple tree at the Park Board site, I found an eggshell that appeared old and stained, and only a week later I saw my first live chicks, fuzzy heads bobbing and weaving above the edge of the nest. Five days later, I saw a third chick. I never did see more eggshells. I learned then that the number of eggshells I found didn't necessarily correspond with the number of chicks, and that although I was now monitoring the birds three times a week, I wouldn't always be the first to find shells. Other animals, and people of course, could carry them off without my being aware they existed.
There were many signs of life in the heron colony: by May 15, chicks were audible in all four trees, and I was finding shells under trees every few days. There were also signs of death - I found chicks that were newly hatched, or shattered eggs with tiny dead chicks under the trees. In the week after May 28 there were verified reports of seven heron deaths, both adults and chicks, due to eagle attacks. I found an eggshell under the tree with frank blood in it the same day I heard of a raccoon raid on a nest in the Douglas fir tree.
Eagle raids took their toll on the Nelson Street tree. By the end of May the nests had been abandoned. At the same time, in the tennis court tree, another new nest (the sixth) was built. New nests were showing up in the Park Board area, near where I had seen the first live chicks. It seemed every time I went out monitoring, there was a new nest to be found, and large maple leaves lay limp on the ground, scattered over the area. The total nest count was up to 18; of these, three were definitely abandoned. There were now five nests in three trees near the Park Board office. It appeared the Nelson Street herons had relocated to a more secure site.
June
The nests and birds were getting more difficult to monitor all the time. Although chicks could be heard in three of the trees, they were almost impossible to see through the large maple leaves, which camouflaged nests and birds alike.
Yet I did see the birds, and was able to make out yet another nest being built in the tennis court tree, to bring the total to seven for this tree. It was a straggly nest, appearing almost like a loosely woven basket. One bird sat comfortably while its mate brought branches at a steady pace. This pair did not stay long, though. The nest was built June 9 and the last day I saw it occupied was June 24.
By mid-June, some of the chicks were so big it was difficult to differentiate them from adults. I could identify the birds as chicks if I could see a line of dark feathers sticking straight up on the head, or see the fluffy but plume-less breasts.
By the end of June, the first chicks I had seen had fledged from the original Park Board location; only two of the original three chicks had survived. The same day I last saw these two chicks, I found new eggshells on the ground under two of the nests in the vicinity.
July
As this month started, the tennis court tree was full of activity - only three of the seven nests were active, but all three nests had at least two chicks. The chicks made a show of practicing flying, jumping short distances and flapping their large wings. They still chattered loudly when the parents brought home food, drawing crowds of curious people, many of whom thought they were either fighting or being attacked.
The Douglas fir tree was quieter. Two active nests remained, each with two chicks. I rarely saw the adults by now, but evidence was there in the form of an occasional fish carcass on the ground.
At the Park Board site, I first heard young chick noises July 4, and saw them for the first time ten days later.
As July draws to a close, my monitoring trips are much shorter. The first chicks have all fledged; my best estimate is that thirteen survived to reach the juvenile stage, and perhaps the two young ones near the Park Board office will too. This would mean a rough survival rate of 15 chicks surviving out of 35 eggshells found on the ground or roughly 43%. Unfortunately, there is no guarantee these young birds will survive their first year away from the nest. They are still at risk from eagle predation. Others will die of accidental causes and from starvation.
Dalyce Epp is a former member of the Board of Directors of the Stanley Park Ecology Society and is a member of the Canadian Society of Environmental Biologists. She began her work with SPES as a volunteer at the Lost Lagoon Nature House and has been observing the herons for 9 years.
If you would like more information on herons, including natural history and the locations of the nests in Stanley Park, please visit the Lost Lagoon Nature House. Taya Maki, our Urban Wildlife Coordinator, has developed a heron display with support from the Labatt People in Action program.
