Quiet sparrows and cacophonous cicadas

Quiet

In March 2020, San Francisco got very quiet. The city was one of the first places in the US to see a surge of COVID-19 cases, and residents quickly retreated into their homes.

As the streets emptied, Elizabeth Derryberry, a biologist at the University of Tennessee, Knoxville, saw an opportunity to study how the cacophony of urban life affects the natural world. In 2015, she recorded white-crowned sparrows around San Francisco and showed that modern birds sang louder, less complex songs than birds in the same area 60 years ago when the city was quieter.

“Across my study sites . . . the noise levels are insane,” she tells Newscripts. “There are birds singing right there at the base of the Golden Gate Bridge. It’s really loud.”

At the start of the pandemic, those sites went silent, and she wondered whether birds would revert to complex songs. After convincing the National Science Foundation to give her an emergency dispensation of funds, she dispatched Jennifer Phillips—Derryberry’s former graduate student who helped gather the original data—to capture bird calls. The National Park Service had closed down the roads in several of the urban parks that Derryberry hoped to sample. But Phillips was allowed to bike in, so she pedaled all over the city to record the sparrows.

When she analyzed the data, Derryberry found that the sparrows were singing songs with lower frequencies in the quieter soundscape. The low pitches normally would be drowned out by the drone of buses and cars. It was as if the reduction in noise gave the birds an additional low octave to compose their songs, allowing for more complexity. Derryberry says the songs with a wider range of pitches contain more information and are likely more effective at communicating a bird’s message.

The research revealed how noisy environments force birds to adjust their behavior. But Derryberry says this natural experiment also showed how quickly efforts to reduce noise, such as building sound barriers and driving electric cars, could benefit the natural world. “It’s hard to get rid of some chemicals; it’s hard to protect the ozone layer,” she says. “Making it quieter is actually not that hard.”

Loud

In the spring of 2024, the midwestern US got very loud. After more than a decade underground, billions of cicadas from the species Magicicada cassini and Magicicada tredecassini emerged simultaneously. The males from these species congregated in trees and, like an orchestra, synchronized their buzzes to produce a wall of sound that overpowered almost any other noise.

Lawrence Sheppard, an ecologist with the Marine Biological Association in the UK, witnessed a similar emergence during a postdoctoral fellowship at the University of Kansas in 2015. “They pop out like magic. They’re orange and black. They make a tremendous noise,” he tells Newscripts.

Even though insects weren’t his normal area of study, he was curious about their behavior. He recruited a group of citizen scientists to record the cicada choruses on their phones in a state park near Lawrence, Kansas. He found that groups of cicadas in trees that were close to each other tended to adjust their rate of calling to match neighboring groups, which indicated that the groups were listening to each other.

It’s not totally clear why they coordinate their calls. Other species, such as frogs, often stagger their calls so that females can identify the most attractive males.

Michael Greenfield, a biologist affiliated with the University of Saint Etienne and the University of Kansas, says his best guess is that joining together increases the strength of the signal, which might help alert females from further away to the group’s presence, benefiting all the males in a group.

While there are seven species of cicadas that emerge either every 13 or every 17 years, only two species sing in unison. Greenfield says the ability to synchronize the rhythm of calls like this is rare. But it’s something cicadas share with humans.

“When you look at organisms that can synchronize like humans, they’re almost all arthropods,” he says. “They’ve developed it independently.”

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