News Archive : 2004-03-22

Surviving the Great Blue Beyond
Herons battle predators -- bald eagles -- to survive, especially during mating season Great blue herons constantly tap each other's bright yellow-orange bills while they keep a careful watch for bald eagles -- sure signs of heron mating season.
 
Kim Westad
Times Colonist
Tuesday, March 23, 2004

The total great blue heron population in B.C. is estimated at 4,000 to 5,000 birds. Although the population of one of the heron's main predators, the bald eagle, is on the rise, the number of herons remains stable, scientists say.

Bald eagles -- and humans -- present the key dangers to the blue heron population, scientists say. The eagles have been known to swoop into a heronry and eat the eggs, the baby herons and even adult herons.

"Ten years ago, finding an eagle in a heron colony was rare. Now, it's rare not to find an eagle in the colony," said Rob Butler, a scientist with the Canadian Wildlife Service and expert in the great blue heron.
Despite this, the heron population appears to be largely stable, say scientists. It also shows that the eagle population, once in danger, is improving.

"In a way, it's a good news story. Eagles are bouncing back .... They've got to eat, too, " Butler said.

So if it seems like there are more herons than usual out there, it's likely just the result of disturbance from eagles and humans.

Because of disturbance, "there's a lot of movement. That makes it appear that there are a lot of herons," Butler said.
The number of herons, with distinctive long legs and neck, may also appear larger because more and more are becoming acclimatized to living in inner-city parks, such as the heronry in Beacon Hill Park, and another in Vancouver's Stanley Park. Herons seen on the Lower Mainland and Vancouver Island are the subspecies fannini. At Beacon Hill, there are about 100 nests just off Douglas Street, delicate platforms of interlaced dry branches 20 metres above the ground.

Both herons and eagles are on the provincial government's "blue list," which means they are vulnerable. They are also listed as being of special concern by the federal Committee on the Status of Endangered Wildlife in Canada.

The total great blue heron population in B.C. is estimated at 4,000 to 5,000 birds, with about half those in southwestern B.C. Eight out of 10 herons on the coast live around the Strait of Georgia, where two-thirds of B.C.'s human population and three-quarters of its labour force lives.

Such close human contact can be a threat to herons, particularly when combined with the eagle increase, Butler said. If chased out of a colony by an eagle, the heron looks for another place to nest. Unfortunately, herons are drawn to the same areas that developers are: near the water, preferably with large trees. With more and more land that they would find appealing being developed, it becomes increasingly difficult for the birds to find a place to live.

Some scientists suggest that there should be no development within 300 metres of the edge of a heron colony and no disturbance in or near colonies from March to August.
Herons tend to live communally in colonies or heronries during those months. The groups can range from a few nests to more than 100, sometimes as many as 40 per tree.

The birds have grown used to a certain amount of human disturbance, but sudden sounds frighten them, like the slamming of a car door, said Michelle Gorman, the integrated pest management co-ordinator with the city of Victoria.
No cars are allowed to park near the Beacon Hill heronry during the courtship and reproductive season.

A proposal for a "heron-cam" will go to council on Thursday. The camera would film from a nearby apartment building, so the public could view and learn about the bird community without disturbing it.

There has been some improvement in toxic contamination, once a prevalent problem for many creatures, including herons. Toxin levels were so high that the egg shell was too thin to sustain the weight of the adult bird sitting on it.
Herons on the Lower Mainland appear to be having more reproductive success than those on Vancouver Island. The number of young in each colony has been falling off in the last few years, Butler said, and are just below the number needed to sustain the current population. In a year, a heron pair need to raise an average of 1.5 young to keep the current population. On Vancouver Island, this number is about one, Butler said, something he thinks is likely attributable to the eagles.

It's also survival of the fittest for heron babies. Weak in the brood are pushed aside by the stronger young birds. If they fall out of the nest, as the weak often do, it's usually their death knell. Herons will not feed young outside the nest.
On average, herons lay from three to five eggs every March or April. Both the male and female incubate the pale blue eggs, the male during the day, the female at night.

Once hatched, the baby herons weigh about 50 grams but reach their adult weight of 2.5 kilograms within two months. If they survive their first year -- fewer than 20 per cent do, according to the Georgia Strait Alliance -- they can live an average of 10 years. Some have lived as long as 23 years.

©  Copyright  2004 Times Colonist (Victoria)