When tourists to Stora Karlso, a limestone-led nature reserve off the coast of Sweden, keeps them at a respectful distance from the many seabirds that call the island home. Like most visitors to wild places, they aim to leave only footprints and only take photos – to glide between the parts of the web of life.
No luck. In an article published this month in Biological Conservation, researchers explained how the sudden absence of tourists on Stora Karlso during the pandemic caused a surprising chain reaction that wreaked havoc on the island’s colony ordinary murmurs, which reduced the population of newborn birds.
Stora Karlso became a nature reserve in the 1880s, after thousands of years of human occupation. Its general murre population – formerly reduced to less than 100 due to hunting and egg feeding – is now about 60,000 birds and is the largest in the Baltic Sea.
Jonas Hentati-Sundberg, a researcher at the Swedish University of Agricultural Sciences and the lead author of the new article, has been studying the colony for 19 years. When he and his team began planning for the 2020 research season, they expected the pandemic to pose logistical barriers: without visitors, fewer boats would operate and the island’s restaurant would be closed.
“Those were our main thoughts,” he said.
However, from their first trips of the year, the end of April, they noticed that the murmurs ‘flew away all the time’, and individuals sometimes disappeared for days. It was a change in behavior, he said, and a sign that something was making the birds more nervous than usual.
The white-tailed eagles of the island also changed their behavior. Normally, seven or eight eagles will spend the winter there, and then leave when the visiting season arrives in the spring, dr. Hentati-Sundberg said.
But without the influx of tourists, they got bitten, and more eagles joined them – sometimes dozens at a time. “They will gather in places where there is a lot of food and few people bother,” he said. “It was their hot spot this year.”
Further observation made the new dynamics clearer: the eagles, freed from the troublesome presence of humans, the murmurs plagued.
Although eagles rarely prey on murres, the seabirds fear them and disperse them at the slightest fly. In one video from May, a distant, broad-winged figure sends hundreds of murmurs honking and stepping off their ridges, like theater-goers rushing to the curtain call from the bars.
It happened over and over. From 1 May to 4 June, birds in one part of the colony were displaced from their nests by eagles for an average of 602 minutes a day – much longer than the 2019 average of 72 minutes.
In addition to time, the murre colony lost eggs and kicked them off ridges during panicked ascents, leaving them vulnerable to hungry gulls and crows. Twenty-six percent fewer eggs hatched in 2020 than was typical for the rest of the decade.
“Emotionally, it’s a little hard to chew,” said Dr. Hentati-Sundberg said.
Researchers around the world have used travel restrictions related to pandemics to study the effects of sudden human absence on the natural world, an event that some call the “anthropause.” A finding like this, where a tourism strike has a domino effect on several species, is ‘fascinating’, said Nicola Koper, a professor of ecology at the University of Manitoba, who was not involved in the research. “It shows how influential our changes in travel have been to the entire ecosystem.”
For Dr Hentati-Sundberg, a summer at a modified Stora Karlso emphasized how strictly we can be intertwined with other species – even if we consider ourselves mere observers – and that ‘we understand our relationships with nature and the idea of ourselves as part of the picture is a more fruitful strategy ”for conservation decisions.
“Stepping back is not an option,” he said. “We’re out there.”