In a few short weeks, legions of green-sheened black waterbirds begin returning to Toronto's shores to nest in dense colonies and cruise the lake for rich bounties of tiny fish. They also bring a mounting wildlife controversy into the heart of the city.
Once virtually wiped out throughout most of the Great Lakes by the ravages of DDT, double-crested cormorants have come back with a vengeance, provoking troubling questions about the stewardship of nature in an ecosystem turned upside down by human intervention.
Wherever they've returned, the large, sleek, hook-beaked diving birds are generating passions. Some hail them as emblems of the lakes' recovery from toxicity, and Canada Post is even putting their image on U.S.-bound stamps. But others revile them as ungainly gluttons despoiling fish stocks and fouling all in their wake - and are pushing for a mass offing of the creatures.
"When these birds move in, they destroy everything in their path," says Greg Farrant of the Ontario Federation of Anglers and Hunters. "Cormorants, on average, eat a pound of fish a day. So you do the math on what kind of impact they're having on various fish species."
Naturalists, however, see the cormorant controversy as a cruel irony in which a native species coming back from the brink is being set up for unwarranted punishment. And they're outraged that the rod and gun lobby - which they believe has oversized clout at the province's Ministry of Natural Resources - is pushing to expand a cull that saw 6,000 of the birds shot last spring in Presqu'ile Provincial Park, west of Belleville, joining similar efforts in a rising number of American states.
But if the government doesn't act, others say they will. A group called the United Fish and Game Clubs of Manitoulin says it has more than 1,000 volunteers ready for their own unsanctioned Victoria Day weekend cull, escalating the vigilante raids that have brought fire and slaughter to a number of Great Lakes colonies over the past decade.
Meanwhile, staff at the Toronto and Region Conservation Authority (TRCA) are weighing the fate of Toronto's burgeoning cormorant population on the Leslie Street Spit. Chief among their worries are whether the newcomers are crowding out other colonial nesters, damaging trees and plants and degrading water quality.
While TRCA's enviro projects coordinator Ralph Toninger rules out a kill-off this year at the Spit, also known as Tommy Thompson Park, he says the Authority, working with federal and provincial wildlife branches, is considering its options. These range from doing nothing to spraying mineral oil on eggs, which suffocates the embryos but tricks parents into wasting the rest of the breeding season in a futile effort to hatch them.
"A consensus and a public process is required first," he says. "We want to come at it from a very holistic approach and address all the park's user groups and the best available science."
Naturalists, however, say they're tired of watching the MNR gearing up to manage resources in favour of a user group hooked on fishing govenment-stocked alien species regardless of the alterations they may cause in the ecology of the lakes.
"Anglers describe cormorants in the most derogatory manner," says Anna Maria Valastro, co-director of the Peaceful Parks Coalition, a grassroots organization focusing on wildlife and park management issues. "They call them roaches. But ecologically, there is no problem with these birds. They are just competitors."
Federal and provincial researchers in the 1990s estimated that the dark, glistening divers, which resemble loons on the water, were taking less than 1 per cent of Lake Ontario's small forage fish. These make up the vast bulk of their diet. Repeated studies going back almost a century show that sport fish and commercial species make up only a small fraction of what they eat, except in limited local situations, particularly at sites where fry are being stocked or at fish farms.
Valastro traces the continent-wide push for cormorant control to demands for government action against over-wintering birds at catfish farms in U.S. Gulf Coast states, where about 10,000 cormorants were shot last year. In 2001, the Great Lakes Fishery Commission, a government-appointed body, also called for stepped-up cormorant management, and in 2003 the U.S. Fish and Wildlife Service handed its authority for the birds' welfare over to 24 states. Michigan and New York State shot some 1,200 cormorants last year.
Ontario launched an ongoing experimental control program in Georgian Bay and the North Channel of Lake Huron after New York officials approached the MNR in 1999 about coordinating efforts. The ministry has oiled thousands of eggs at about 40 colonies for the last three years.
"We are unwilling to intervene (with widespread control measures) until there is evidence of significant effects" on Lake Huron's fish and other ecosystem elements, says MNR senior avian biologist Bruce Pollard. "It's a really complex issue, and there are certainly polarized views on this."
Though some anglers have raised concerns, says Toninger, the TRCA does not regard cormorants as a threat to local fish stocks. The birds are mostly eating alewives, little sea fish that were introduced in Lake Ontario by the 1880s and have become more plentiful than anything else in the Great Lakes system, he explains. "It's a testament to the alewife's abundance" that there are so many cormorants, says Toninger.
The prodigious droppings produced by the diving birds' extremely dense congregations, however, are another matter. The acidic guano usually kills the trees in which they nest in three to 10 years, along with much of the vegetation below. The trees on one of the Spit's peninsulas are already gone, leaving the cormorants to nest on the ground. The park's nearly 1,000 pairs of tree-nesting black-crowned night herons - themselves relative newcomers to Lake Ontario, originally attracted by the area's huge colony of ring-billed gulls, on whose eggs they feed - have been forced out to other parts of the Spit.
Naturalists believe there is plenty of room in the park for all species to keep moving on to new areas with trees, allowing natural regeneration take its course at sites they've vacated. Cormorants, they note, only nest on very isolated points and islands, where they concentrate so densely that they take up relatively little space.
"It's just a question of aesthetics," says the Toronto Ornithological Club's Glen Coady, who's been birding on the Spit since he was a small boy 35 years ago. "At the Spit, what you have is a community of willows and cottonwoods that are younger than I am."
Central to the issue is the paradox that the Leslie Street Spit is a human creation, gradually built up with dumped landfill from construction since 1965. But it's been claimed by a succession of plants, trees and wild creatures, becoming one of the city's most important nature preserves.
The Spit's night heron population has increased in tandem with the cormorants over the past five years, points out Coady, who believes the park is well on its way to becoming the most diverse colony of herons and other waterbirds in Canada. Within the past two years, a handful of great blue herons and great egrets have started nesting there, after the cormorants were well established.
"Cormorants are actually catalysts for other birds to arrive," says Peaceful Parks' Valastro, noting that, as at the Leslie Street Spit, green herons, terns, gulls and many other colonial species also commonly nest at the same locations as cormorants. "Nature is not a green museum. It's not stagnant. It evolves," she says. "Every time we manage, we lose knowledge."
Double-crested cormorants were once uncommon on the Great Lakes, nesting mainly in far northwestern Ontario, around the Lake of the Woods. For unknown reasons, they expanded or increased breeding on Lake Superior in the early 1990s. Poorly understood changes in the Great Lakes ecosystem, including the sharp decline of predatory fish species, are thought to be at least partly responsible for the birds' movement east. They began nesting on Lake Huron by 1931 and on Lake Ontario in 1938. By the late 40s, their numbers prompted culls.
Unfortunately, says Coady, the scattered culls probably masked the effects on the cormorant population of the introduction of DDT as a pesticide after the second world war. "We would have got the message faster from cormorants than from eagles, ospreys and peregrine falcons if we hadn't been shooting them," he says, noting that cormorants are more readily victimized by the pesticide than almost any other bird.
DDT derivatives and PCBs moved up the food chain through fish accumulated in the tissues of top predators like cormorants, herring gulls, bald eagles and ospreys, causing them to produce eggs with shells too thin to survive or chicks with high rates of abnormalities. Cormorants photographed with hideously deformed criss-crossed beaks became the poster birds for Great Lakes contaminants. Populations plunged, and by 1973 there were only about 10 nesting pairs on Lake Ontario.
Fishing bird populations eventually recovered after most uses of DDT
were banned in 1974. "Basically, the rebound of this bird is a good-news story," says Coady, noting that it reflects a steep reduction in toxins in the Great Lakes ecosystem. "This is an absolutely stunningly beautiful bird," he adds, citing the cormorant's striking blue-rimmed emerald-green eyes and the contrast of its yellow bill with the bright-blue interior of its mouth, which is held agape in greetings between mates.
In 1990, cormorants began nesting on the Leslie Street Spit, and the colony quickly grew. Last year there were a conservatively estimated 23,000 birds on three peninsulas of the Spit by the end of the breeding season.
But in response to pleas that wildlife be allowed to do its thing, Toninger says the reality is that
"the Spit is not a natural location and is adjacent to Canada's largest city. So the area surrounding it does not function as a natural system." The way the Spit is being built - the creation of artificial fish-spawning shoals, duck ponds, tern nesting platforms, bird boxes and shoreline modifications, and the undertaking of invasive species control programs - demonstrates that "all aspects of the park are either directly or indirectly managed," he says.
"We are managing [the Spit] as an urban wilderness site, and cormorants are part of that urban wilderness. They are part of the diversity of the park and part of the reason for it being a unique area," says Toninger.
On a wider scale, says the MNR's Pollard, the conundrum is whether after "humankind has wrought incredible change on the Great Lakes ecosystem," we can simply step back and let cormorants pick over the results.
Pollard says concerns over the cormorants' impact on other colonial birds and vegetation were also the main reason behind last year's cull at
Presqu'ile, which has Ontario's largest colony of egrets, a rare nester here. "It comes down to whether, as stewards, we are willing to let cormorants push herons and egrets off the site," he says. "We have to weigh the value of the resource with the expected degree of damage."
Groups like the Ontario Federation of Anglers and Hunters back the government's stand, saying their predominant concern is the overall impact of cormorants on the ecosystem. Valastro, however, sees the argument as a front to protect sport and commercial fishing interests. While anglers vilify cormorants and ignore the impact of their own activities, she says, the introduced sports fish species they promote, such as Pacific salmon and rainbow trout, are massively stocked each year and suppress native predators, including lake trout and whitefish.
Overfishing, in fact, is thought to be at least partly responsible for the cormorants' great numbers. Together with the introduction of sea lampreys into the Great Lakes and the loss of spawning grounds, it caused steep declines in the numbers of lake trout and other large predatory fish between the 30s and 50s. At the same time, alewives and rainbow smelt, another tiny introduced ocean fish, were also spreading exponentially through the lakes with little to keep them in check. When cormorants began to recover from DDT, there was much more to eat than ever before.
Alewives themselves also harm native fish populations because they compete with and eat the young of yellow perch, walleye (also known as pickerel) and lake herring (or cisco). In addition, the alien fish have an enzyme in their gut that, after they are eaten by lake trout, causes the trout to produce hatchlings that die of thiamine deficiency.
In fact, an alewife collapse in Lake Huron and Georgian Bay - the lowest numbers seen since they first spread into the area in the 1940s - due to recent severe winters has been followed by big rebounds in yellow perch and walleye, says David Reid, MNR lake management supervisor for Lake Huron. Lake herring also seem to be coming back, and lake trout are starting to reproduce naturally again in some areas.
On top of everything else, the cormorant population of the North Channel and Georgian Bay has fallen by a third, to less than 20,000 nesting pairs, since the alewife collapse. "We don't think (the alewife collapse) is attributable to cormorants. We think it's the other way around," says Pollard.
Over the past five years, the waterbird's overall numbers have also stabilized on Lake Ontario and Lake Erie, though Pollard says that may be due in part to management efforts at Presqu'ile and in New York State. He thinks cormorants are probably running out of ideal nest sites on isolated islands and points. "It may be, like any species occupying a new habitat, that after initial rapid growth, as they fill up their new environment, they reach the carrying capacity."
Tim Tiner's latest book, along with Doug Bennet, is Wild City: A Guide To Nature In Urban Ontario, From Termites to Coyotes (McClelland and Stewart).