The Stanley Park Heronry Journal

June 21, 2009

These young siblings are almost as large as their parents and will soon leave the nest.
Photo by Martin Passchier

If you are out observing the heronry in Stanley Park you will notice a flurry of activity in and around the oak, maple, and London plane trees.  These activities naturally revolve around food, both getting food and becoming food.

You will see a steady flight of heron parents, making their flight path to foraging grounds – reminiscent of aircraft taking off and landing in a busy airport.  Feeding rates are extremely high right now and the chicks, which began life at a mere 50 g, are now nearing their parents’ size of 2-2.5 kg.  Many are in the last ¼ of their 60-day nestling dependence on adults.  Therefore, they need LOTS of food.

A great blue heron catching a goldfish.
Photo by Martin Passchier

Where are the parents getting all of this food?  During the breeding season the intertidal areas are the restaurant of choice.  The breeding season coincides with a tidal "window of opportunity."  In May and June, 70% of low tides occur during the day.  Herons forage in the rocky near-shore waters, from wharves and sandy beaches, as well as in freshwater habitat and ornamental ponds.  One desirable food source is in underwater eelgrass meadows.  Rob Butler of the Canadian Wildlife Service (1995) found there were more than 12 million fish in one hectare of eelgrass meadow, which is made up of marine vegetation nearshore that serves as breeding and feeding grounds for many fish species, such as striped perch and pipefish.  Herons are a wading bird.  They feed in shallow water and spread out their long toes for support.  When a fish is detected, the heron freezes like a statue, holds its neck in a spring-like S-shape, and with a quick motion stretches out to catch its prey.  In our seashore and wetland waters, flounder, perch and pipefish are common prey, but also crabs and bullfrogs.

At this time of year SPES and Parks’ staff keep an extra close eye on the colony, as some of the youngsters leave the nest before they are fully able to fly.  This young heron was seen hanging around below the colony until it was finally able to take wing.
Photo by Martin Passchier

Interestingly, food appears to be abundant in the heronry this season, in spite of its late start because of cool weather.  Heron breeding season also corresponds with high sea surface temperatures which ensure that enough fish are available for females to gain the weight needed to lay up to five eggs.  Although not all the eggs will have resulted from coupling with her present mate (extra-pair copulations are common), these birds will remain seasonally monogamous.  The abundance of food is also evident by the high within-nest survival rates this season.  Many nests are sporting 3-4 large teenaged chicks with their characteristic "punk" style head plumage.  Siblicide (when older, larger chicks kill the smaller, younger ones) is not as common this season as it was last year.  Many chicks are surviving to the age where they now exhibit "branching," an activity where they take their first tentative steps or hops away from the nest to adjacent branches in the tree.

Two of the culprits who have been raiding the colony.  The bald eagle spent several days harassing herons and the raccoons seem to come almost every night.
Eagle photo by Maria Morlin

What is worrying, however, is the high mortality of chicks from another source: predators.  The chicks are on their own while the parents are off feeding.  This makes them vulnerable to predation.  One predator in recent weeks has been a large bald eagle, who has flown in and sat in the colony for hours beside alarmed chicks not more than a few feet away.  There have also been reports of owls in the colony at night hooting along with the many cries of protest from the chicks and adults.

Probably the most serious predator, however, is the raccoon, whose population numbers are artificially inflated in Stanley Park due to feeding by humans.  This is problematic not only for breeding birds, but also for the raccoons themselves who will die off from disease due to overcrowding.  Whereas eagles may take one chick from a nest, raccoons are wiping out all the chicks from single nests.  Next season, we will investigate the possibility of installing predator guards around the base of the trees to prevent raccoons from climbing them.

On the bright side, the herons are valiantly working to bring up the remaining chicks to fledging age.  There are even a few incubators still present with eggs and new hatchlings.  These herons may be starting over after their first nest failure.  Unfortunately, a couple of nests have had their second failure, and have abandoned the colony for this season.  Seeing new hatchlings this late in the season accentuates the astounding contrast in morphology between age classes.  The little "newbies" are nearly naked with sparse patches of grey down on their sides, wings and back, but the older chicks have brown feathers and ruffled crowns which will later turn grey.

Adult great blue herons can be distinguished by their white crown with black stripes down the sides, long chest plumes, grey-blue wing coverts and black epaulettes (shoulder pads).  The bluish colour is a result of powder down feathers beneath the contour feathers that the herons crumble with their bills and spread through their plumage to clean fish oil from their feathers.

Juvenile: Grey crown and grey wings flecked with brown; lacks shaggy neck and back plumes and black face plume.

Adult: White crown and face; black plume extending from above the eye to beyond back of head; blue-grey body with black shoulders.

Conserving heron populations is crucial to keep our delicate marine and terrestrial ecosystems in balance.  Herons are an important part of the food web linking bacteria, plankton, clams, crabs and fish with mammals and birds.  Although herons in the Stanley Park heronry are habituated to humans, they will have difficulty withstanding predation from too many sources.  In particular, we need to be vigilant about not feeding raccoons and other wildlife, as this seriously interferes with the natural balance.

By Maria Morlin, veteran SPES heron monitor

UBC Great Blue Heron Colony Update

The UBC heronry has expanded dramatically this year.  Last year, there were 9 active nests, of which all but three either survived the winter or have been rebuilt.  Now there are 21 confirmed nests and possibly another two.  Six of the new nests are close to the older nests, and five of these are within a few metres of the C. K. Choi building on the UBC campus.  The other new nests are short distance to the west of the original colony, close to the Nitobe Garden.  Interestingly, all the 2008 nests and adjacent additions are in Douglas fir trees, while the new nests to the west are mostly in western red cedars.

By June Ryder, UBC Heron colony monitor

May, 2009

Photo by Martin Passchier

The heron colony is extremely active these days, with various stages of colony development going on: herons are building nests, incubating eggs, and brooding the young chicks.

With 141 nests, the colony size is similar to last year (146 a year ago), but the numbers are not static yet.  As the birds make last-minute changes, some nests are being abandoned while new ones are being constructed.

Raccoon predation is likely a cause of nest abandonment.  Recently, nearby residents have heard heron distress calls during the night and monitors have observed that several nests previously occupied by incubating birds are now empty.  Fortunately, it’s still early enough in the season for the birds to lay new eggs For the Birds and the Bees and raise a clutch of chicks.  Predation by raccoons may also have been the reason that fragments of the blue-grey eggshells were first seen beneath the nests during early April.  Chicks were not heard until May 1; they may have been up to a week old by then.

These days, the cheeping and squawking of heron chicks is almost constant.  On May 17, rooftop monitors observed 53 chicks and 10 eggs out of 40 visible nests (three of these were not occupied).  The chick ages ranged from one day to perhaps three weeks.  In the remaining nests, the tireless parents are laying and incubating eggs and tending to chicks.

As always at this time of year, monitoring of the colony gets more difficult as the trees leaf out.  The maple trees near the Park Board office are the earliest to leaf, followed by the oak trees along Park Drive.  The London plane trees are the last to leaf out, so these nests are still visible from the ground now – but difficult to see from the rooftop.

May and June are probably the best times to catch a glimpse of the young chicks; their fuzzy little heads can just be seen bobbing above the nest sticks.  And, watch for a parent flying to the nests – if it is bringing food for the chicks, the little ones will make their presence known!

By Dalyce Epp, Volunteer heron monitor

April 18, 2009

A Pacific great blue heron in Vancouver’s West End.
Photo by Martin Passchier

The heron colony is off to a late but great start this year.  Snowfall thwarted earlier attempts of the Pacific great blue heron (Ardea herodias fannini) to start courtship and mating.  Birds were seen around the heronry as early as February 20.  March 13, however, seemed to be the real start, when twenty herons were spotted in the trees.  By April 5, numbers had increased to 165, and a number of eggs were also observed.  By this date a total of 121 nests were counted, with 95 occupied.  Last year at the same time, there were more nests (142 in Apr. 2008) but fewer occupied, and fewer adults present (113 in Apr. 2008), even though colonization started a month earlier.

Although the season started late, the herons laid eggs very soon after their first arrival.  Timing is important, since herons must time the raising of their young with optimal feeding conditions, which coincides with the productive spring tides.  Herons feed in tidal areas and when they have lots of mouths to feed they need the best conditions possible to get enough fish.  In a good year, a pair of herons can raise 3-4 young but on a bad year maybe only 1-2.  A disadvantage to late hatchings is that young herons get less time in the productive summer months to get big and strong to survive the winter.

Stanley Park Ecology Society heron monitors are excited about the new season, and look forward to watching the herons progress from building nests to raising families to watching the young ones learn how to fly.

A pair of herons tending their newly laid eggs.
Photo by Maria Morlin

Although the female is the master weaver, the male retrieves the twigs for initial nest building.  The males continue to bring twigs to the nest after the eggs are laid and after hatching occurs.  We're now seeing existing nests disappear as they are dismantled, and watching couples trying to build new nests from scratch (not as easy as it seems).  This is an interesting behaviour as they are very detailed at arranging their nest, and weave twigs in such a specific way, even without opposable thumbs!  Courtship is always very intriguing with the ritual of bill clapping, beautiful breeding plumage and darker bill colour during the mating season.

A couple of observations of concern so far this year are raccoons and balloons!  Raccoons are a comical but not entirely welcome sight as they sleep and groom in heron nests.  So far, they don’t seem to have a big effect on the heronry, although they are predators of heron eggs.  Also, one day a large bunch of balloons floated from above and lodged into one of the trees.  The herons briefly abandoned their nests, but are all back to incubating eggs (hopefully the eggs weren’t exposed for too long).  Balloons are hazards to wildlife, and should be kept indoors.

Even colourful balloons won’t deter these adaptable urban herons.
Photo by Martin Passchier

Counting herons, nests and eggs has its challenges and rewards.  Monitors counting from the roof of an adjacent building are challenged by depth perception as it is difficult to identify individual tree limbs out of the dense stand.  Without leaves it is a little easier.  These photographs show the difference between early and late season.  Also, the wind can be biting on hands holding binoculars.

These two photos taken by Maria Morlin are of tree "B" in the heron colony.  This photo shows the bare trees in early spring...

...while later in the season the leaves restrict our view to most of the nests.

If you are observing the colony from the ground, be sure to look for monitors and have a chat.  They enjoy talking to people and answering questions.  Colony visitors are very enthusiastic and have many different perspectives.  It is great that people take the time to consider the birds’ role in nature and the environment.

By Maria Morlin, veteran SPES heron monitor

Map of Stanley Park Heronry, March 2009

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