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Many of you kept an eye on the Stanley Park heronry this summer. We asked local resident and biologist Dalyce Epp to share her Heron Journal with our readers and reminisce about the drama of life and death in the treetops.
The Heronry Journal Archive:
- 2008 Entries:
- 2007 Entries:
- 2006 Entries:
- 2005 Entries:
- 2004 Entries:
The Stanley Park Heronry Journal
July 8, 2008
A great blue heron lands on a branch.
Photo by Martin Passchier
The Stanley Park heron colony is shrinking. Some of the oldest chicks have finally taken wing and the gangly immature birds can be seen teetering on nearby trees and branches ready to follow suit.
A heron in flight.
Photo by Martin Passchier
The next step for these birds will be to find their way to nearby feeding grounds to practice fending for themselves. Catching small fish in a big ocean is not an easy thing for the young birds, and they will have to try and fail many times before honing their new skills. The young fledges may follow their parents to preferred feeding grounds or they may set off on their own. Several immature birds have already been seen nearby at Lost Lagoon and Beaver Lake and others have been observed trying their luck along the beaches, especially in the area between Second and Third Beach in Stanley Park. To help the fledges get the best start possible, it is important to leave them undisturbed: remember that dogs are not permitted offleash at most of the local beaches.
Some birds are still not quite ready to leave the colony, these venture on to nearby branches and even into other nests. Some nests that contained 2-3 chicks last week now contain 4-5. As soon as an adult bird draws close, a loud uproar of squawking chicks greets them and it is hard to tell which of the chicks belongs to that adult.
Two of the nests in tree "H" were recently attacked in a late-night raid. Witnesses heard screams coming from the direction of tree "H" and later observations proved that at least two nests had been preyed upon. One witness believes she heard an owl as the nests were attacked. Owls are a predator of heron nestlings but raccoons are also common around the colony and have attacked chicks in the past.
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.
If you have still not made a trip to see the colony, now is a great time. Most of the chicks are quite large and visible through the tree branches. The roaring sound of feedings and the frequent flights in and out by the parents make this an exciting time. By the end of July many of the chicks will have left and the numbers will drop dramatically.
June 10, 2008
A great blue heron chick waits for a returning parent to bring a fishy meal.
Photo by Martin Passchier
Chicks are between 1 day and 6 weeks old!
The Stanley Park great blue heron colony is still growing and now has a total number of 149 nests. As some prospective parents are building new nests, others have recently hatched chicks, and a majority of nests contain chicks that are already several weeks old.
Heron monitors watch the colony weekly from the ground and from a nearby rooftop.
Many gawky "teenage" chicks can be seen teetering precariously on the edges of their treetop homes. Of the estimated 250 chicks currently in the colony, the oldest are about 6 weeks old and will soon be ready to begin the process of fledging from the nest.
Frenzied feeding and sibling rivalry are the two most recent developments at the colony. Both heron parents make endless day and night trips to local seashores and marshes to find food for their youngsters. Upon each return they are greeted by a nest of demanding chicks. Each time the parent enters the nest, the chicks begin a deafening display of bill clapping and squawking as they lunge at the parent begging for food. The largest chicks grasp the parent’s bill and yank violently to induce regurgitation. If there is enough food to go around, the other chicks will have a chance to feed until it runs out. Adult herons can often be seen sitting calmly away from the nest in a nearby tree. They seem to need time to recover from the intensity of the feedings or to prepare themselves to enter the nest once again.
Three or four chicks can sometimes survive to fledging age, but often siblicide results in the survival of only one or two.
Photo by Martin Passchier
The herons have a system to ensure that they will successfully produce the correct number of chicks without knowing how much food will be available in advance: The herons practice "asynchronous hatching" whereby eggs are laid at staggered intervals but incubation begins immediately so that they hatch at slightly different times. The oldest chicks will also be the largest chicks and the ones most likely to survive. No one knows exactly why this is, but presumably they do this so that in times of abundant food they can produce many chicks, and in times of less food they will have fewer but stronger chicks to take care of. The younger, smaller chicks are not just out-competed for food by their larger siblings but are also pecked at or even pushed from the nest. This process called "siblicide" is seen in many species, especially raptors (like bald eagles) and other wading birds (such as cranes). During our weekly observations we have seen nests that contained four small chicks quickly result in a nest with one or two large chicks. Last year our monitoring records showed that about 60% of the nests started with 3-4 hatchlings and ended up with 1-2 fledglings.
An interesting fact to note while you are watching the herons at this time of year is a difference in defensiveness amongst the adults. Herons change the way they defend their nest site as the season progresses. When they are establishing their nest, the area they defend is about 2m, when they begin incubation the defense radius decreases to about 1m, and by the time the chicks are hatched and growing, the parents seem not to defend the nest at all (Butler, 1997)**. This change in behaviour is likely an adaptation to reduce extra-pair copulations and is regulated by changing levels of the hormones testosterone (produced early in the season) and prolactin (produced during incubation).
At this time of year, due in part to the high incidence of siblicide and because fledgling chicks often fall to the ground as they practice for their first flight, it is not uncommon to find young herons under the colony. If you find a young heron that you believe is injured, or in need of help, please call the Vancouver Park Board Park Rangers at 604-718-5849. Please note that they can not always respond immediately, but will get to the heron as soon as possible.
Map of Stanley Park Heronry, June, 2008
May 11, 2008
A heron with a downy chick in the nest.
Photo by Martin Passchier
The heron colony has some new additions!
The Stanley Park great blue heron colony is growing busier every day as many chicks have newly hatched. The downy grey chicks sport fuzzy mohawks atop their tiny heads and sway their necks about comically. The parents take turns gathering food and brooding the young. When the adult returns from hunting, the youngsters squabble over the regurgitated fish. The fight for survival has begun.
The colony is not as large as it was at this time last year. On May 9, 2007 the colony had a total of 181 nests; this year it only numbered 135 on May 9. However, herons can still be seen gathering sticks from the trees around the colony and the forested areas of Stanley Park in order to build new nests. The new heron parents are also gathering sticks to reinforce their nests. The nests are solidly built from the beginning, but they need to grow over the season, as they will eventually have to hold up to four or five birds at one time!
We are currently closely monitoring 40 nests that we will use as a sample of the whole colony. All of the 135+ nests in the colony can not be monitored throughout the season because so many of them become obscured by leaf cover. So far this season, several of the sample nests have disappeared after having fallen or been dismantled by herons scavenging sticks for other nests. One pair has abandoned its nest containing three eggs. The nest may have been abandoned due to harassment by predators (observed frequently this season) or one of the parents may have died. Almost all of the herons in the remaining nests are either incubating eggs or raising newly hatched chicks.
[ The latest Heronry Map can be found below ]
March 31, 2008
A heron in flight.
Photo by Martin Passchier
The Heron Colony is active again and parents are incubating eggs
The Stanley Park great blue heron colony is buzzing with activity as herons form pairs, build nests, and begin laying eggs.
The herons arrived back at the colony on February 24th this year (10 days later than last year) and the first eggs were seen on March 23rd.
Number of nests in the Stanley Park heron colony
The colony is not yet full as only 85 of the approximately 150 existent nests are currently occupied. Since the herons arrived this February, the number of nests has decreased (see figure) as some nests have fallen in recent storms and the herons have dismantled others in order to repair their nests.
Last week was a tense time for the colony as bald eagles raided the nests on several occasions. More than one eagle spent several hours flying from tree to tree eating the freshly laid eggs. Luckily, the herons did not abandon the colony and when we checked the nests the following weekend, many pairs had laid more eggs. Eagle harassment is one of the leading causes of heron colony abandonment in the Lower Mainland, and the Stanley Park colony is likely made up of herons that have left other colonies for the same reason. In 2004 there were 70 active nests in Stanley Park and the number rose to 170 in 2005. This change in our colony coincided with the abandonment of the UBC and Point Roberts colonies.
[ The latest Heronry Map can be found below ]
February 27, 2008
The herons are back!.
The Stanley Park great blue heron colony is active again for the 2008 breeding season
Herons were seen congregating around the neighbourhood and in the nest trees over the last couple of weeks, but as of February 24 some of them have staked their claim to their preferred nests. Male herons are usually the first to arrive, followed closely by females who choose a mate for this year’s attempt at producing chicks. The males currently at the colony have selected previous nest sites that they will build upon and repair once they find a suitable partner. Mating displays are exciting to watch as the herons flap their wings, clap their bills and appear to dance for one another.
This "species of special concern" is especially sensitive to disturbance early in the nesting season. Although this colony has become habituated to the sounds of cars, people and other noises in the city, the herons can become frightened and even abandon the colony if a novel disturbance takes place close by. It is also important to note that these birds need their space, so they should not be approached or fed, and dogs should be leashed in the Park.
Soon after the herons form pairs and repair or build new nests, they will lay 5-7 light blue eggs and begin incubating. Last year, the herons occupied 183 nests in 24 trees and produced approximately 350 fledglings by the end of the season. Stanley Park Ecology Society monitors have noticed that the herons may be scoping out some trees that have not been previously nested in, indicating that the colony may expand this season.
Map of Stanley Park Heronry, February, 2008
