Rachel Carson and the Cormorants

In the 1970s, cormorants were in freefall. The once prolific birds seemed destined for extinction. The mass die-off was the work of a silent, invisible killer - which was also, weirdly, a Nobel prize winner. 

It was also a very good reminder of the fragility of ecosystems and the unintended consequences of any change we make to our environment. And if it wasn’t for one single-minded woman, the cormorant - and who knows how many other species - might never have made it.

In 1939, we thought we’d found a miracle. A chemical compound that worked as an incredibly efficient and safe insecticide. Its name was, deep breath, Dichlorodiphenyltrichloroethane, and we embraced it with our usual lack of foresight. Admittedly, it was a lifesaver. Paul Hermann Müller - who didn’t discover it but did prove its efficacy as an insecticide - eventually won the Nobel prize for that work in 1948. By that point it had been proven out in WWII, preventing insect transmission of typhoid, yellow fever and malaria in soldiers and civilian populations.

You could buy Dichlorodiphenyltrichloroethane by its household name, DDT, by 1945. It quickly became an invaluable part of agriculture in the US - and was pretty liberally used by anyone with a bug problem, farmer or not.

But DDT didn’t get a free pass from everyone. And one of its most vocal critics was Rachel Carson.

Carson was already a respected marine biologist who had transitioned to writing full time in the 1950s. She penned a trilogy of books about the biology and ecology of the sea that were bestsellers and award winners. But the book that would secure her legacy was still to come.

She was already concerned about the casual, widespread use of dangerous chemical compounds - including DDT. But her tipping point came in 1957, with an effort by the US government to eliminate the spongy moth by spraying huge swaths of land with DDT from airplanes - indiscriminately, including privately property.

Carson flung herself into her work, compiling studies that showed the deleterious effects of widespread chemical use on both the ecology and people. More and more ominous research was being published revealing its unintended consequences, including a much greater risk of cancer. 

And as Carson fought to prove it, she was diagnosed with cancer herself. In the 11th hour of writing her book she underwent a mastectomy - which no one knew about. She hid her diagnosis and procedure completely, fearing it could make her appear biased. 

Silent Spring, finally released in 1962, had a profound impact - and not just on pesticides. It’s credited as being one of the seminal works that sparked the environmental movement, the fundamental idea that human action can cause massive interference and damage in natural systems.

Carson herself died just two years later. Already weakened from breast cancer treatment, she caught a respiratory virus which lead to a heart attack. She never got to see just how powerful her final book would be.

The echoes of her work were as vast as the creation of the Environmental Defense Fund and the Enivronmental Protection Agency - and the wholesale banning of DDT, which Carson had referred to as an ‘elixir of death’. Beset by fierce opposition and criticism by chemical companies, not to mention her own worsening health, she held firm until the truth won out.

The real impact and damage of DDT is insidious. It doesn’t present itself readily, which is why it took such a huge effort to get it banned. It may kill insects outright, but the way it leeches into us and other animals - like the cormorant and many birds of prey - is more subtle. 

The whole reason DDT was meant to be so safe is that the concentrations being used were so small that no animal bigger than an insect needed to worry. But that’s where the creeping effect of ‘biomagnification’ comes into play.

We probably all have a basic understanding of a food chain (more accurately ‘web’ but for our purposes): the sun and soil feed plants which are eaten by invertebrates and herbivores which are eaten by predators who eventually die and nourish the soil. 

At each stage of that process, any chemical compounds in the ecosystem are being concentrated more and more. The layers of the food chain are like a pyramid with each successive step needing more biomass below it to survive. So when a fish eats a whole bunch of insects, the DDT present in each individual insect is concentrated in one fish. And when a cormorant eats a whole bunch of fish, it’s compounded again. So the ‘ambient’ amount of a chemical in the environment is meaningless when nature has an efficient way of loading it up in predators.

DDT doesn’t straight-up kill birds when they eat it. Again, its effects are much more subtle. DDT is insoluble with water, but soluble in fats - that’s what makes it so damaging to living things. It won’t mix or disperse to safe levels in water but it’ll grab on to fats in an animal’s body.

Once it’s inside, it does a very weird, specific thing - it inhibits calcium production. This can have all kinds of effects, none of them good. But the most important for birds like the cormorant is, it leads to much thinner eggshells (which are made of calcium).

Those thin-shelled eggs are more prone to damage, defect and stillbirth. It’s a sobering reminder of the breadth of unintended consequences. If we sprayed a field with DDT and birds dropped out of the trees it would be easy to make the connection and ban the practice. But linking DDT to declining birth rates due to thin eggshells is a much more winding path, harder to prove, harder to convince people of - and while we try to sort it all out, we’re still spraying the stuff everywhere.

The proof is clear to see, however. Cormorants along with many, many other predatory species saw sharp declines in the 1970s as the mass of DDT that had been unloaded on the environment worked its way up the food chain. And with the banning of DDT starting in 1972, that process could be - and was - reversed, as species like the cormorants surged back.

DDT was just one factor in the decline of the cormorant - but that makes Rachel Carson and her work all the more amazing. Because she wasn’t just responsible for targeting one insidiously lethal pesticide. She helped turn our global consciousness to how much our actions could truly upend the natural order, and began a fight to re-evaluate our relationship with our environment which is still being fiercely fought today.