credit Steve Adams
This first part of the fable, that of the pie, you may know. It’s the story ofEctopistes migratorius, the passenger pigeon. It was once the most abundant bird in North America; its population would have reached, in the middle of the XIXe century, between three and five billion people. Yes, you read that right: billions, not millions. A distant cousin of the mourning dove of our cities and suburbs, the pigeon lived in the central and eastern United States and in southeastern Canada (Manitoba, Ontario and Quebec).
In spring and summer, large flocks of the species, numbering in the thousands, visited the St. Lawrence Valley to feed on acorns of oaks, samaras of elms and maples and cereal grains. Flights so dense, so extensive, according to the testimonies of the time, that they would have obscured the sun for entire days. Like a river of feathers in the sky. It is also said that when the pies perched, the branches of the trees broke under the weight of so many birds. No one might have imagined that one day the species would disappear from the face of the Earth. This is what happened, however, because it was hunted ruthlessly, with guns and in many other ways, for example by spreading large nets or by cutting down the trees on which the individuals perched to then kill with sticks. all those who might not escape. The species declined rapidly and eventually died out in September 1914, when its last representative died, a female named Martha, kept in captivity at the Cincinnati Zoo.
The second part of the fable, the one concerning the tick, you probably don’t know. A few years ago, researchers hypothesized that the disappearance of the pie played an important role in the progression of a disease that now affects humans in North America, Lyme disease. How is it possible ? Quite simply because they were overabundant at the time, the pies competed with many other species that fed on fruits, nuts and seeds, including the white-footed mouse. The disappearance of the bird in the natural ecosystems of the continent would have greatly favored the mouse which might, therefore, count on unexpected quantities of food. In the following decades, its population would have increased considerably.
What is the connection between mice and Lyme disease? The small rodent in question is a so-called reservoir species: among other things, it harbors the bacteria responsible for the disease, Borrelia burgdorferi. And here comes the blacklegged tick, the species responsible for transmitting the disease from mice to humans: in the larval stage, the tick drinks the blood of mice and other micromammals; in the adult stage, it attacks large mammals, indiscriminately, such as deer orHomo sapiensthus spreading the disease in humans.
Lyme disease is now one of the most common ailments south of the Canadian border; its incidence exceeds HIV. Previously confined to the central and eastern United States, it is gaining ground every year. Quebec is no exception: the number of cases reported annually has increased in ten years from 32 (in 2011) to 463 (in 2021).
The disappearance of a species is often accompanied by repercussions that are difficult to predict in the long term on the other species with which it is related. It will have taken a hundred years to measure the ecological consequences of the overabundance of the white-footed mouse and, by extension, on the progression of the tick and the Lyme disease associated with it. Chance has here, in a way and through tortuous ways, punished humans for their past actions. Revenge is a dish best served cold.
The moral of this fable? We will always be surprised by the complexity and extent of the links that unite living beings on our little blue planet. A galaxy of endless interrelationships.
Michel Leboeuf is a writer, biologist and general manager of the Lanaudière Ecosystems Conservation Trust.
