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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.
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Heron Colony Updates
June 17, 2010
The heron colony is a buzz with activity lately as the first fledglings have begun taking flight!
They grow up so fast!
Photo by Martin Passchier
Many large chicks now occupy the colony and are constantly receiving food from their parents and even a few eggs are still being incubated.
Last year, the colony experienced a higher incidence of predation from raccoons which climbed up the trees and fed on chicks and eggs. This year, raccoon predation has decreased, due to the installation of predator guards in a cooperative effort between the Vancouver Park Board and Stanley Park Ecology Society staff and volunteers. Nevertheless, eagle attacks from the air have been on the rise. A volunteer who lives next to the colony hears the drama unfold nearly every morning! This is a concern for the future of the colony, as persistent eagle attacks have led to colony abandonment in other areas (such as Beacon Hill Park colony in Victoria in 2007).
Despite all these disturbances, many of the herons have successfully raised healthy chicks and many of the young birds can now be seen hopping from branch to branch, testing their wings as they prepare for their first flight and a life on their own. Several of the nests that were predated early in the season are still active as the parents laid a second clutch of eggs. There is a good chance that these chicks will survive, due to the early start of this season and several new downy grey chicks were spotted already this week.
Three fledglings
Photo by Martin Passchier
The final numbers for overall nest success (the number of successful nests out of all nest attempts) and productivity (the number of successful chicks per nest) are not in yet, but preliminary information shows that out of the 124 nests in the colony, about 69% were successful. Out of the successful nests, about 1.8 chicks were produced per nest for a total of about 157 chicks fledging from the colony this year. We will continue to monitor the entire colony as well as our sample set of nests in the coming weeks to ensure accurate estimates are obtained and to determine the success of the "re-nesters."
Stretch!
Photo by Martin Passchier
Be sure to visit the colony if you are in Stanley Park. It is located outside the Park Board head office at 2099 Beach Avenue.
March 24, 2010
The Pacific Great Blue Heron Returns to Stanley Park for Another Season
Time to start building a new nest!
Herons, herons and more herons! In spite of the commotion the Olympics caused, not to mention the rainstorms, wind and weird weather, the herons came back to the colony early in February. Signs of their impending arrival included an increase in heron sightings around Stanley Park. According to one of the Sunday morning bird walk regulars, "I�ve seen more herons in Lost Lagoon and around the sea wall than all winter, as if they were gathering for something."
On February 6, three herons were seen gathering on a building close to the Park Board office, but that was a false alarm. They disappeared for about a week and then on February 15 all of a sudden there were 26 herons in the trees. This occurred about a month earlier than last year when snowfall was the flavour of the month of March!
Ah, breeding season here again!
The breeding season of the Pacific great blue heron (Ardea herodias fannini) in British Columbia is influenced by sea temperature, tides, and the availability of small fish such as three-spined sticklebacks, bay pipefish and starry flounders (Butler 1997). It takes a lot of energy to produce eggs, and herons need to acquire that energy in preparation for the egg-laying period (3-5 eggs laid 2-3 days apart). It takes ten days for egg formation, and 27 days for incubation. The reason for the herons� early arrival may well be the recent El Niño. An El Niño raises sea surface temperature by only a degree or so on average, but significantly affects the migration of fish in our coastal waters.
The first heron surveys of the season were conducted on March 7, 2010 by SPES staff and volunteers. At that time there was a total colony count of 134 nests with 79 occupied (59%) and 135 adults present. Of the 39 sample nests that are surveyed regularly, 23 (59%) also appeared active. All of the birds were building nests and forming pair bonds and none had begun incubating yet.
Helping to protect the herons from raccoons are these metal predator guards
In January of 2010, Vancouver Park Board and SPES staff and volunteers collaborated to install predator guards around the heron nest trees. This was done to prevent the high incidence of raccoon predation which occurred in the colony during the 2009 breeding season. Raccoon populations in this area of the Park are very high and these animals ate about 32% of the heron chicks in 2009. The metal predator guards are working well so far, although some of the more persistent raccoons have still found their way into three of the trees.
Written by Maria Morlin and Robyn Worcester
Photos by: Martin Passchier
Map of Stanley Park Heronry, March 2009
Colony map by Dalyce Epp
