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Quiet Spring: Fifty years since Rachel Carson

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A Chimney Swift at its nest.

"The sedge is wither'd from the lake, and no birds sing." – John Keats, 1819, La belle dame sans merci

In 1962 I was only eight years old, but I listened with fascination as my mother read segments of Rachel Carson's seminal book, Silent Spring, to the family after dinner. My parents were naturalists and early environmentalists and I gravitated to nature even as a preschooler. Like so many people of the Silent Spring generation, we read (or in my case, listened to) Carson's book with growing alarm. The natural world that we loved was being poisoned and degraded by indiscriminate pesticide use, particularly uncontrolled and escalating use of the pesticide, DDT (dichloro-diphenyl-trichloroethane). The birds that my family spent every weekend observing in marshes, forests, parks, and reserves were being poisoned. Raptors such as Bald Eagles, Ospreys, and Peregrine Falcons were vanishing, their ever-thinning eggshells crushed as soon as the parents attempted to incubate them.

Carson's book galvanized not only me and my family, but a whole generation. Environmentalism was born and by 1970 agricultural use DDT had been banned in Canada, followed shortly thereafter in 1973 in the United States. Other countries followed suite and by 1984 DDT and most other organochlorine insecticides (the chemical family that DDT belongs to) were banned throughout the word (limited so-called "vector application" of DDT for the control of fleas, for example, continues to be permitted in many jurisdictions). Populations of eagles, ospreys, and falcons began to rebound. The environment was seemingly on the mend. Or was it?

A recent study by a team of 10 Canadian scientists from Trent University, the University of Ottawa, Queens University, and Thompson River University, spearheaded by Joseph Nocera, casts light on what transpired and its continuing repercussions on the natural world.

Chimney Swifts are delightful birds that superficially resemble swallows. They breed across eastern and central North America, migrating south through central America and the Caribbean to winter in northwestern South America. They are so-called aerial insectivores, meaning they feed by catching flying insects 'on the wing.' They are also fast disappearing. Since 1968 when the North American Breeding Bird Surveys began to monitor populations of birds on the continent, chimney swift numbers have decreased by 96 percent. This dramatic decline has lead the Committee on the Status of Endangered Wildlife in Canada (COSEWIC) to categorize them as a federally threatened species. And Chimney Swifts are not alone. Many other small insect foraging birds have exhibited sizable decreases in populations -- and these declines continue. What's going on? Nocera and his colleagues believe they have uncovered a piece of the puzzle.

Once upon a time, chimney swifts used to roost and nest primarily in hollow trees, but since logging practices removed many such sites, chimney swifts found the best possible alternative -- chimneys. Nocera's colleague, Christopher Grooms, discovered a disused chimney on the campus of Queens University that, between 1928 and 1992 (when it was capped), served a major home for thousands of swifts that roosted in it each night. What they left behind was guano, and that heap of excrement turns out to be a scientific goldmine.

Why? The layers of guano are a historical record of what the swifts had been eating -- and more. Measuring isotopes of carbon and nitrogen in the guano provides information about the source of the food and on what is called its "trophic level," in other words, how high up the food chain the insects the swifts were consuming were. Importantly the investigators were able to measure levels of DDE (dichloro-diphenyl-dichloroethane) in the guano, a stable compound formed by the decay of DDT. Examining this data the scientists discovered something of considerable significance.

The insecticidal properties of DDT were only discovered in 1939 and by 1945 it was in widespread use in North America for a large number of agricultural and other applications. As pesticide use increased the diet of chimney swifts in Kingston changed markedly from approximately 75 per cent beetles (Coleoptera) and 20 per cent true bugs (Hemiptera) to approximately 30 per cent beetles and 60 per cent true bugs.

So what, you might think: an insect is an insect is it not? But not so. Beetles can provide a greater caloric food value for swifts whereas true bugs, being on average higher up in the food chain, bio-accumulate more pesticides such as DDT or DDE. So, swifts were getting less food value for the insects they were eating and being exposed to higher levels of insecticides. And this was also reflected in the levels of DDE in the swift guano. In later years, as DDT use declined, the ratios began to return to normal but even when DDT was banned in 1973, the beetle/true bug ratios did not return to pre-insecticide levels, nor, indeed, did DDE disappear from the insects swifts were consuming.

What does all this mean? Nocera and his colleagues are careful to point out that more than just pesticide use and its impact on insect populations has affected chimney swifts; climate change and habitat loss have both been identified as contributing factors to their disappearance. However, this study provides some compelling evidence that pesticide use has affected populations of insect-feeding species such as swifts (and there are many other birds, such as wood warblers, that have shown similar patterns of decline). Such pesticide-induced dietary changes, and their nutritional consequences, may have significant impacts on bird populations, and such impacts can continue long after the chemicals in question have been banned. DDE continues to persist in the food chains and chimney swift populations have not recovered.

Here's the stinger: this issue isn't just a sad historical footnote, another illustration of how prescient Rachel Carson was a half century ago when she despaired of a silent spring, with no birds left to sing in the vernal field and forests. While pesticides and their byproducts such as DDE continue to persist in the environment, new dangers now face insect-feeding birds, in the form of climate change. Nocera and his colleagues note that "The problem has become increasingly compounded by the recent reductions in availability of an insect prey as a result of climate-induced changes in the phenology of insect emergence." What does this mean? Simply that continuing climate change is altering the times when many insects hatch or emerge from hibernation. The breeding biology of birds has evolved in lockstep with the phenology (i.e., the seasonal timing) of their environment such as the availability of food to bring them into breeding condition, feed their young, and provide them with energy reserves for migration. Many recent studies are showing that climate change is upsetting this precise coordination of timing, to the detriment of species that are unable to adapt to these changes.

What was the response to the publication of Silent Spring? Carson was subjected to a massive attack by the chemical industry lead by giants such as Monsanto, American Cyanamid and Velsicol who subjected her to derision, questioned her scientific credentials, called her a hysterical woman and threatened her with lawsuits. Compliant media and the U.S. Department of Agriculture followed suit. However, United States President John F. Kennedy directed his Science Advisory Committee to investigate. Their investigation vindicated Carson's claims and lead to the establishment of the Environmental Defense Fund that launched court challenges to ban the use of DDT. In 1971 the courts ordered the Environmental Protection Agency to deregister DDT.

Now, with the shadow of DDT still hanging over their well-being, the future health and survival of many populations of birds is threatened by the spectre of climate change? Will there be politicians of the calibre of John F. Kennedy ready to stand up against commercial and industrial interests in their defence? Recognizing the threat, will Canada's Environment Minister, Peter Kent, step up to the plate and increase funding for research, monitoring, and remediation programs to address the impacts of climate change? Will Prime Minister Stephen Harper champion the cause of vanishing songbirds? It seems unlikely.

Many sectors of Canadian society are still in shock, reeling from the recent budget cutbacks. One department hit hard is Environment Canada, particularly its programs to monitor climate and environmental change. The National Round Table on the Environment is being eliminated. The Polar Environment Atmospheric Research Laboratory (PEARL), perhaps the single-most important research facility in the world in monitoring climate and environmental change in the high arctic is permanently closing as a result of funding cuts. And these cuts come on top of earlier cuts announced in August 2011 that slashed $222.2 million in spending and eliminated 1,211 jobs resulting in the elimination of the Clean Air Agenda, Air Quality Health Index, and Species at Risk programs. Researchers in the areas of climate change and clean air were cut in half, and the current round of funding cuts will reduce them even further.

So should we resign ourselves to springs, every one quieter than the last? Thus far, the track record of the Harper Conservatives does not auger well for a melodious future. Swifts require the help of some political friends to get by, but so far the federal government does not appear to be singing their tune.

Christopher Majka is an ecologist, environmentalist, policy analyst, and writer. He is the director of Natural History Resources and Democracy: Vox Populi.

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