This was a quiet spring for the residents of the bay area, as the Covid-19 was trapped inside the house to make us wait, worry and wander.
But outside, our birds rediscovered their sexiest serenades. The stage was all his.
Comparisons of the first time before the spring time Tuna closes and the sound of avian songs show that birds respond quickly when humans rejoice.
They sang more softly – and the songs were faster, lower and faster with a more romantic range, according to the study, published in the Thursday issue of the journal Science.
The sound level of bird songs during shutdown has dropped by more than four decibels; Because decibels are measured on a logarithmic scale, the songs were about a third softer. No longer forced to compete with the human epidemic, the birds also lowered its pitch by 160 seconds per second.
“It highlights how much impact humans have on wildlife behavior – and how quickly wildlife can react when human behavior changes,” said Elizabeth Deriberry, a leading researcher in animal communications at the University of Tennessee.
“People take care of nature as soon as they get out of the way.”
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In April and May, Derryberry stopped at her Knoxville home with her cooks, as bored and frustrated as the rest of us were.
Then she saw a photo of the empty Golden Gate Bridge nearby, which did not show the movement of vehicles at post-1954 levels – reversing more than half a century of noise pollution.
“It’s so quiet in San Francisco!” She thought. And wondered: “Do birds sing differently?” Unable to travel, she enlisted the help of former graduate student Jennifer Phillips, who was doing postdoctoral work at the Cal Poly San Luis Obispo.
Phillips quickly filled the sound equipment and ran to San Francisco, the Marines and East Bay in search of birds growing in lupine, poison oak, age shi and coyote shrubs.
The research is part of a new field of acoustic ecology that explores how nature struggles between the sight of our urban sounds and adapts itself to hearing. Previous work has shown that frogs, insects and whales change their behavior in an increasingly noisy world. Species of birds that are very adaptable to city life, such as starlings, have been found to be awake early in the day to defeat the rush hour cockroaches.
In particular, the team discovered white-crowned sparrows, common creatures that are beloved by scientists for the flexibility of their songs. The simple chorus of the species – a clear whistle, then humming on different pitches or a series of trails – varies regionally, and may change over time.
They also sing in dialects; 10 different patterns have been calculated in the bay area. To whistle with a whistle or a trail, the San Francisco Sparrow looks distinctly different from the Marine Sparrow, which looks different from the former two Sparrows.
Scientists have amassed a vast archive of two Area Sparrow songs, spanning several decades and safely stored at the California Academy of Sciences. In the Golden Gate Park recordings of the 1967 Summer Love Festival, anti-war activists can be heard chanting behind a bird choir.
Singing is important for the survival of the bird, helping to find its mate and save the territory.
David Luther, a fellow researcher at Derryberry and George Mason University in Virginia, has documented that in noisy places, cherries migrate to loud songs that cannot be heard. And they sing on the pitch rather than the low frequency of traffic jams.
But this comes at a price: they can’t produce fast trails on wide frequency bandwidths – informative music that’s too sweet for suitors.
“It’s like a boom at a cocktail party. You’re talking small, not deep, “said Deriberry. “Or political rallies, where people conspire, not policy.”
Every day, Philips enhanced the Marantz digital recorder, the Larsen Davis sound level meter, a rangefinder for calculating distances, and the receiver, with a high-end microphone mounted on the Parop .la.
In the Presidio of San Francisco, he noted above Fort Point, a place that is usually filled with the roar of traffic from the Golden Gate Bridge. She also went to Point Isabel in Richmond, near the busy Highway 580, popular with chatty walkers, cyclists, dog-v-cars and boaters. Then, in search of nature, he turned to the scrub land of the wild Point Reyes National Beach.
His first challenge was to distinguish Sparrow’s song from other birds’ symphony. Then she had to find the bird. She noticed how it was coping. And she had to sneak around in front of him – positioning her tool, ideally, at the level of the beak.
It was an attempt to have patience, calm precision and focus. Sometimes, when things were perfect in terms of sound, birds flew.
Her sound files were compared with recordings made during April and May 2015. They were accompanied by historic historical recordings – old real-to-reel tapes that were preserved as digital dioteps.
The team found that this spring’s sparrows, in exposure to low background noise, display a loud “display” in which the amplitude of the sound is reduced and the minimum frequency of the sound is reduced.
Notably, birds sang low at the Richmond site, not recorded since the spring of 1971.
The silence also changed how people understood what they heard. Although the birds sing more gently, their songs travel twice as long.
Scientists will continue their research to see if birds ‘behavior will change again in response to our ever-louder sounds – and if next year the chicks will be able to learn their parents’ songs, or adapt to their new and more noisy world.
They also hope that their discovery will encourage human behavior to change.
“Animals can recover if we give them time to do it,” Phillips said. “If we reduce our noise pollution – driving less, using electric cars, changing the way we build our roads – hopefully they will be more successful in urban environments.”
