With many schools and businesses closed to prevent the spread of coronavirus, fewer cars are on the road. Even normally busy highways are relatively empty. So in some places, it’s quieter outside.
That might have an impact on birds and other animals that are making their own kind of noise this time of year.
One thing the coronovirus can’t stop is the arrival of spring — early signs like the calls of frogs, or spring peepers. Another is the chorus of songbirds. But this year, even longtime listeners are hearing something different.
"We were stunned at how quiet it was," said Don Kroodsma, a retired UMass Amherst ornithologist who was walking with his wife recently near the Connecticut River at the end of a work day.
"This is probably the typical UMass rush hour — where there's just no UMass rush at this time. Everybody’s staying home," he said.
If a professional listener like Kroodsma heard a difference, what might animals notice? And would a soundscape with fewer cars change how they behave?
Wildlife biologist Paige Warren of the UMass Amherst Department of Environmental Conservation has reviewed research on how human-generated sounds impact animal communications. She talked about the challenge different kinds of birds normally face when they sing near the rumble of cars.
"If you have a high-pitched, 'tweety tweet tweet' sound, then it might get through better than if you have a low-pitched kind of sound," Warren said, imitating the call of a dove. "So if you're a dove, it might be harder to get your message through the traffic. And then when there's less traffic, it might be easier to be a dove."
The messages birds send with their calls and songs include alarms to alert other birds to predators, a "get-out-of-here" sound, defending nesting territory, and songs that serve as advertisements seeking a mate.
David Luther, a biologist at George Mason University, studies how birds adjust how they sing to contrast with background sounds made by humans. He said each species does it differently.
"In general, species tend to sing a little bit louder in the presence of human noise," Luther said. "Others will change the pitch or frequency of their song so they don't tend to sing in the lower frequencies of their song, down here. And they’ll sing up here, sometimes instead," he said, demonstrating a change in pitch. "Other species have been shown to actually change the structure of their song, so they have different types of notes when it’s louder human noise."
Luther said less human-made noise, at the moment, could have a positive impact — for instance, less stress on birds, or access to more territory.
"Places that they wouldn't go when it's usually really loud," Luther said. "So they might expand their habitat use or territory size a little bit, so they can get more food, and potentially even newer access to mates."
Luther said the song a male sings may even sound better.
"Better, more beautiful, that will get more females to respond to it than the song he would be singing when there is human- made noise around," he said.
But if coronavirus restrictions are not long-term, could there still be an impact? Luther said birds will adjust their songs temporarily, in response to the shift in human-made noise.
"We've seen that when the noise of human-made noise is quieter, the birds will often change their songs back to lower frequencies, or not shouting as much," he said. "But then, when the human-made noise gets louder — and this can just be over the course of five or 10 minutes, let alone days, weeks and months — they’ll change their songs to accommodate that noise."
Less car traffic may also make the sounds of nature accessible to more people.
Paige Warren has studied bird species in neighborhoods with different incomes.
"Wealthier neighborhoods have higher numbers of bird species," she said. "And wealthier neighborhoods tend to be quieter, have less traffic noise than more impoverished neighborhoods."
With emptier roads now, there might be a change for some humans.
"This might open opportunities for people in otherwise noisy neighborhoods to potentially hear some of the nature around them," Warren said.
More nature for more people — quieter soundscapes for birds to communicate more effectively — may be a short-term silver lining to a period of human isolation.