During the worst of the pandemic, when humans took refuge in our homes to escape the virus, many animals roamed the cities. Although a good part of the videos about panthers, deer or badgers stepping on the asphalt turned out to be false or recorded before the coronavirus, that exceptional situation has served scientists to analyze the flexibility of animal behavior. A work of 175 scientists following almost 3,000 mammals in the hardest of confinement has allowed them to confirm that they moved and moved closer to the roads. But the increase in mobility only occurred on longer journeys and in areas where the lockdown was strictest. The authors of the work, published in Science, believe that not only human infrastructures harm wildlife, so does the mere presence of humans.
Human constructions are among the most studied impacts on the natural environment. On the borders of Asia and Europe there are more than 30,000 kilometers of fences. On the European continent alone, one million artificial barriers interfere with the natural course of rivers. And half of Spain is less than a kilometer from a road. Highways and other artificial incursions into nature, such as railways, have a triple negative effect: they erect barriers, they take humans and invasive species to the depths of the wild and, as the drama of the lynx shows, they multiply the outrages. But what really affects animal life, infrastructure or its use by humans? It is not easy to disaggregate both impacts. Only on exceptional occasions, such as the creation of the Chernobyl exclusion zone, has it been possible to study the change in animal behaviour in the absence of humans. Hence, scientists have taken advantage of the months of confinement due to the coronavirus to estimate its true impact.
The work published in Science shows that the animals came up to 36% closer to the roads. To measure it, scientists tracked the movements of 2,300 animals of 43 species in dozens of countries thanks to the GPS collars they wore. But this greater proximity to the roads only occurred in areas with a high human footprint, that is, with a strong presence of infrastructure, agriculture, urbanized environments, and in regions where the confinement was more severe.
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The researchers used two other metrics: the total distance traveled in 10 days, on the one hand, and the journey made in one hour, on the other. Representing the two extremes of the mobility pattern. Marlee Tucker, a researcher at Nijmegen's Radboud University and lead author of the study, says that during the forced confinement of humans "animals travelled distances up to 73% longer than in the same 10-day period of the previous year, when there were no lockdowns." This comparison with 2019 is one of the strengths of this work. They have been following the same animals for several years, so they have been able to compare with the times when there was no coronavirus. For example, in a study also published in 2018 they already detected that where there are humans, animals move less.
"The animals traveled distances up to 73% longer than in the same 10-day period last year."
Marlee Tucker, researcher at Radboud University Nijmegen and lead author of the study
As for short trips, the opposite happened: the animals reduced their movements. "The response was variable between individuals and species. Some covered longer distances and others shorter, but on average there was a decrease of 12%," Tucker said in an email. "We don't have the data needed to measure the impact of this change on animals, however, for some, it could be a pretty significant decline." This change in the pattern could be due to the fact that, in the absence of humans, the movements to avoid and flee them decreased between February and May 2020, coinciding with the hardest confinement, according to the authors of the work.
During the lockdowns, large mammals crossed the roads naturally. MARK GOCKE
The Spanish Nuria Selva, researcher at the Polish Academy of Sciences, spent the entire confinement in the Białowieża National Park (Poland), one of the last virgin forests in Europe. As co-author of Tucker's research, she highlights that changes in animal mobility patterns depended on the degree of confinement: "The reduction was smaller in moderately urbanized or semi-natural areas. In those areas there were still people, like in the parks, where human presence increased by more than 200%," he says.
Beyond mobility, human presence can also affect the physiology of animals. In a work yet to be published, Selva has found that cortisol levels – an indicator of stress – were lower in bears and chamois in the Tatra Mountains National Park (Poland) during the months of human confinement.
"A road where no one passes is not a barrier, the barrier is traffic, it is us"
Nuria Selva, researcher at the Polish Academy of Sciences and the University of Huelva
Selva highlights another great contribution of this work: "It has allowed us to separate the impact of human infrastructures and humans themselves. A road where no one passes is not a barrier, the barrier is traffic, it is us." A few years ago, between 2013 and 2015, Boise State University biologist Jesse Barber conducted a series of experiments with traffic. He recorded the noise of several highways and took it to various natural environments where there was no asphalt. Their results showed that on so-called ghost roads a large percentage of the birds disappeared. During the pandemic, the opposite phenomenon was observed: birds sang quieter and communicated better during confinement.
The biologist of the University of A Coruña Alejandro Martínez Abraín highlights the statistical power of the work, but maintains that changes in movement patterns have only been observed in areas with the largest human footprint, "in very severe confinement conditions and at the extremes of animal mobility". He also recalls that they have not studied the presence of wild animals in cities.
A raccoon walks through a nearly deserted Central Park in Manhattan on April 16, 2020 in New York City. The image was reproduced by those countries where the confinement was stricter. JOHANNES EISELE (AFP)
"Not all animals are interested in having little movement of people," says Martínez Abraín about the impact of infrastructure and human presence. "For example, with respect to roads, many prey species are interested in having a lot of movement, because that inadvertently does what is called in ecology the scarecrow effect, scaring away predators." He continues: "Great bustards are interested in being close to roads, because they avoid the wolf and hunters, who cannot shoot near a road." And it has many more examples: starlings that cluster at crossings, where there can be no hunting. The kites that fly over the route of the railways looking for food. The rabbits that breed next to the highways. The bears with young who go down to the villages to avoid the male who could kill their young. Or the wolves that do not cross the highways, "pass them over, by the change of direction, like humans," recalls Martínez Abraín.
For the professor of the Galician university, changes in animal mobility patterns are not a matter of confinement: "We have to go back to the abandonment of the field. Animals have been losing their fear of humans for six or seven decades, of urbanites who are not going to do anything to them. This has not been changed by covid, it has been changed by the abandonment of the rural. What happened during the pandemic is that they took another step in their approach and we have realized something that I already saw happening."
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