Vancouver Sun June 7, 2001

Eagles threaten heron nesting grounds

The raptors are eating eggs, killing birds Larry Pynn Vancouver Sun Great blue heron colonies across B.C. are coming under attack from a growing bald eagle population, raising fears that the herons -- already classified as "vulnerable and at risk" in the province -- could be in serious trouble within 15 years.

"It's really troubling," Canadian Wildlife Service biologist Rob Butler said. "In the 1960s and early '70s, it was a big deal to find an eagle nest. Now, they're everywhere."

The extent of the eagle's threat to herons is revealed in a master's thesis by Ross Vennesland of Simon Fraser University's behavioral ecology program.

Vennesland spent 550 hours in 1999 observing about 1,500 nests within 31 heron nesting colonies, (representing up to one-third of the total B.C. population) in the Strait of Georgia, Lower Mainland and on Vancouver Island.

His conclusion: eagles targeting heron eggs or young were responsible for the abandonment of 12 of those colonies, which contained 58.5 per cent of all nests.

"They swoop right in, and sometime hop from nest to nest," Vennesland explained from his Victoria home. "They smash eggs (typically three to four per nest) and slurp up what they can.

"I've also seen them flying away with large young, or a fetus in their bill. It's definitely a brutal scene to watch, kind of shocking, because everyone likes eagles. I do, too. But this changes your opinion of them, to some degree."

Eagle populations in B.C. are up 10-fold since the 1960s due to several factors: a ban on pesticides such as DDT and a reduction in organochlorine chemicals such as PCBs, dioxins and furans; the switch to steel shot from toxic lead shot, minimizing the risk to eagles feeding on poisoned waterfowl; and greater protection for eagles and their nests in Canada and the U.S.

Whether the increased predation on heron nesting colonies is simply a reflection of the larger eagle population is not as clear. Eagles might be switching to herons because of reduced stocks of salmon and other fish. Or eagle numbers might be unusually high due to human factors such as garbage dumps in which the raptors are known to feed.

The largest single colony of great blue herons in North America -- 450 nests -- is located within barely one hectare of forest reserve on the U.S. enclave of Point Roberts, near Tsawwassen, and is considered a shared population with Canada.

Ann Eissinger, a contract biologist with Nahkeeta Northwest, said this week she knows of bald eagles killing at least 11 adult herons this spring while they sat on their nests. "That's unprecedented. I've never observed that in any colony. It might have been caused by one renegade being very aggressive."

But there have also been sightings in the Lower Mainland and the Gulf Islands of eagles attacking and killing adult herons away from their nests, hitting them in mid-flight and drowning them in the water.

Eissinger believes the eagle population in the region has reached its nesting capacity and that juveniles in particular might be turning to herons due to a collapse of in-shore fish stocks.

"There is a larger issue we need to pay attention to," she said. "Eagles are shore-dependent. They'd prefer to be out squishing mud between their toes and catching fish than hanging out at the heronry."

But human influences don't stop with overfishing. While Vennesland found that nesting herons could habituate to humans (loud, unusual noises excepted), he found that predation by eagles was greatest in colonies close to people.

Whether there are more eagles around people due to garbage dumps or other sources of food, or whether another factor is at work is unknown.

"That was really curious," he said. "There's no direct influence, just people walking around. The herons weren't responding to them, and they're not doing anything untoward to the herons.

"But there is some interaction. Either the eagles are attracted to humans or the herons are just a little bit scared (of humans) but don't show it and the eagles can get in there easier. Human influence can be more insidious than you think."

Butler also said that while eagles pose a direct threat to herons, humans are a compounding influence, because as a result of development there are fewer protected wood lots into which the herons can disperse for nesting.

"It's troubling when humans are part of the formula," he said.

Added Vennesland: "The worry with the herons is that while the numbers look fairly stable right now, this productivity decline won't show up for another 10-15 years at least. We're quite worried about the future."

Still, no one is suggesting a cull of eagles, even in light of a probable reduction of herons in the coming years, given there are so many unknowns.

"I haven't heard any calls like that," Vennesland said. "That would be premature."

Chilliwack is one community trying to reverse the trend with the establishment this fall of the 120-hectare Great Blue Heron Nature Reserve, including 10 hectares of land formerly owned by the Department of National Defence alongside the Vedder River at Greendale.

An interpretive centre will be established, with fencing to prevent an overly enthusiastic public from getting too close to the approximately 100 nests. Ironically, an active bald eagle nest is also situated within the reserve.

"It's not too intrusive, actually a benefit to the colony," said Jerry Spencer, director of parks and recreation for Chilliwack. "It will keep other eagles away."

A heronry near UBC has about 130 nests, and a cursory look shows it is still functioning, although perhaps at a reduced level. However, a colony of 100 heron nests at Duncan and at least 125 nests at McFadden Creek on Saltspring Island were abandoned this spring.

"We're all pretty devastated," said Nina Raginsky, coordinator of Saltspring's Waterbird Watch Collective. "It was the community's colony. One lady broke into tears. A lot of people think of them as their herons."

A grassroots campaign four years ago generated $250,000 to purchase five hectares of land. The community asked private landholders to maintain a 300-metre buffer and to not make loud noises during breeding, Raginsky said, but efforts failed when two property owners cleared land near the site, putting stress on the adults and making the heronry more vulnerable to eagles.

"It was the cumulative impact of human disturbance," she said. "It was like their front door being taken off. It was too much for them."

According to Environment Canada, about 9,000 great blue herons live along the coast from Washington to Alaska. Up to 80 per cent of those live in the southern part of the Strait of Georgia and northern Puget Sound, centred near the mouth of the Fraser River.

Since the 1960s, the breeding eagle population in B.C. has increased at an average annual rate of six per cent. A 1994 inventory estimated that 15,000 eagles (9,000 on the coast and 6,000 in the Interior) breed and 30,000 winter in the province, mostly in the Georgia Basin.

Comments about this article? Send an e-mail to the writer.

-- Lars (larsguy@yahoo.com), June 08, 2001

Answers

Brought to you by Repug's ignorant, lazy, stingy, mean-spirited environmental policies

-- (herons@risk.Dumbya_did_it), June 08, 2001.

so have an eagle at thanksgiving.give the turkey's a year off.

-- al-d. (dogs@zianet.com), June 08, 2001.

I hate to draw the thread away from the heron loss, but did you ever see one of those raptors in the sky? There was one flying [if you can call it that] about two blocks from my home recently. It was so still that I thought it was a kite at first. I pulled over my car so I wouldn't kill myself or someone else with my concentration on the sky. It just hung there, in space, wings spread, soaring on the updrafts/downdrafts. FINALLY, it flapped its wings and flew off into the horizon.

-- Anita (Anita_S3@hotmail.com), June 08, 2001.

Probably a hawk, they are common. Yeah, that's cool how they can soar for hours on invisible thermals with barely a wing flap. Looking for mousies, rabbits etc.

-- Lars (larsguys@yahoo.com), June 08, 2001.

Animal rights has many conflicts these days. I see where PETA wants to prevent China from having the Olympics because of their treatment of dogs and cats (they eat them).

Like dogs and cats don't eat other living creatures?

-- Lars (larsguy@yahoo.com), June 08, 2001.