The great auk, a large, flightless bird with a black back and a white belly, once lived across the North Atlantic—from Scandinavia to the eastern coast of Canada. Since prehistoric times, humans hunted these great animals, which could reach two-and-a-half feet in height, for their meat and eggs. But around the early 16th century, when European seaman discovered the large auk populations of Newfoundland, the killing of the birds reached rapacious levels. “Enormous numbers were captured,” writes Encyclopedia Britannica, “the birds often being driven up a plank and slaughtered on their way into the hold of a vessel.”

By the mid 19th century, the great auk had disappeared. And now, a study published in the journal eLife seeks to answer lingering questions about the birds’ demise: Did humans alone drive auks to extinction? Or was the species already declining due to natural changes in the environment?

Hoping to shed new light on the great auk’s extinction, a team of researchers sequenced the complete mitochondrial genomes of 41 birds, using specimens held in museums, reports Gizmodo’s Ryan F. Mandelbaum. The remains dated from 170 to 15,000 years old, and represented individuals from across the auk’s former geographic range. The researchers were looking for signs—like a loss in genetic diversity—that might indicate the species had been declining before intensive hunting began around 500 years ago.

But the team did not find evidence that great auks were slowly dwindling due to the pressures of environmental change. “[T]heir genetic diversity was very high—all but two sequences we found were very different," Jessica Thomas, a postdoctoral researcher at Swansea University who led the study while a Ph.D. student at Bangor University and the University of Copenhagen, tells Victoria Gill of the BBC.

The researchers also looked at GPS ocean current data and conducted population viability analyses, which assess the probability of a population going extinct within a certain number of years. Using simulations for population sizes of one million and three million mature birds during the period before intensive hunting began, the team determined that harvest rates of up to nine percent of the population would have been sustainable. But a rate of ten percent, combined with a five percent egg harvest rate, led to extinction in most of the simulations. A harvest rate of 10.5 percent led to extinction within 350 years for all of the simulations.

As an example, the researchers note that if auk populations had reached two million—one million adults and one million juveniles—before the 16th century, killing 210,000 of the birds annually would have driven them to extinction within 350 years. And it is likely that more than 210,000 auks were slaughtered each year. The fishing grounds off Newfoundland alone used to draw fleets of between 300 and 400 European ships, according to the study authors. In one instance, contemporary reports indicate, 1000 auks were caught and killed by two fishing vessels within half an hour.

“[I]f each of the 400 vessels in the region spent only half an hour a year harvesting great auks at this rate,” the researchers write, “that would already correspond to 200,000 birds a year.”

There are several drawbacks to the new study. For one, the sample size of 41 auk specimens was small. Researchers were only able to sequence the birds’ mitochondrial genome, which represents just one type of genetic marker. And while the researchers’ DNA analyses suggest that auks were not declining before humans began to hunt them intensively, “this doesn't mean that we've provided solid evidence that humans alone were the cause of great auk extinction,” cautions study co-author Thomas Gilbert, professor of evolutionary genomics at the University of Copenhagen.

“What we have demonstrated,” Gilbert adds, “is that human hunting pressure was likely to have caused extinction even if the birds weren't already under threat from environmental changes."

Even considering these limitations, the study offers a sobering look at just how quickly humans can decimate a robust species. “[I]ndustrial-scale commercial exploitation of natural resources,” says co-author Gary Carvalho, professor of zoology at Bangor University, “have the potential to drive an abundant, wide-ranging and genetically diverse species to extinction within a short period of time."