And since this massacre, populations of these black-and-white birds, often confused with little penguins, have shown few signs of recovery, suggesting long-term changes in the food web as well as a new balance of the ecosystem.
An “alarm bell”
“We talk a lot about the decline of species linked to temperature changes, but in this case, it is not a long-term result,” explains Heather Renner, biologist in a nature reserve in the Alaska and co-author of the study. “To our knowledge, this is the largest documented episode of wildlife mortality during the modern era,” she and her colleagues insist in the study.
These results should serve as a “wake-up call,” explains the researcher, because global warming, attributable to human activities, makes heat waves more frequent, more intense and more lasting.
A long and extended wave
About forty centimeters high, Common Murres are nevertheless considered robust birds, due to their thin wings allowing them to travel great distances to find food and their diving abilities.
But this heat wave, which stretched over two years and affected a vast area of the northeast Pacific Ocean, from California to Alaska, seriously affected them. During this episode, 62,000 emaciated, dead or dying birds were found on thousands of kilometers of coastline.
The cause, according to the researchers: a reduction in the quality and quantity of phytoplankton linked to the heat, which thus affected fish such as herring, sardines and anchovies on which guillemots feed.
This phenomenon was also coupled with an increase in the energy needs of large fish also due to the heat, which then entered into competition with murres for the same prey.
A reassessment of the balance sheet
“We knew then that it was a significant problem, but unfortunately we couldn’t really quantify the effects,” recalls Heather Renner.
Initial estimates put the number of dead birds at around a million, but a more in-depth analysis released Thursday based on data from 13 murre colonies found the death toll was four times higher. “The situation is much worse than we thought,” reports Heather Renner.
Other animals affected
The heatwave also affected populations of Pacific cod, king salmon and humpback whales. But while these species suffered the effects, others emerged unscathed, experts point out.
For example, thick-billed murres, which often nest on the same cliffs or ledges as common murres, have been spared, perhaps because of their more adaptable diet, says Heather Renner.
For murres, however, the fallout persists. Nearly ten years after the heatwave, their colonies show no signs of recovery, and the losses may well be permanent. This is explained by the long-term decline of some of their prey, but also by their survival strategy which is based on their collective life.
These seabirds group together in gigantic colonies to protect their eggs from predators like eagles and seagulls. With the drastic decline in their population, this defense system has been weakened.
Conservation measures coupled with those necessary to combat global warming could offer a chance to these threatened birds, believes Heather Renner. Fighting certain predatory and invasive species, such as foxes and rats, is another of the solutions considered.
