Adjustments to life in a COVID-19 world are not limited to humans. Some birds also have changed behavior.
White-crowned sparrows living in the San Francisco metro area didn't adopt extraordinary behavior. They simply reverted to normal.
It's about traffic noise, masking song notes, forcing the bird to invest more energy into its message.
Research published in the journal Science reported that the observed birds seemed to react to the drop in human noise, vehicular traffic in particular.
After decades of sacrificing song quality for higher volume, these sparrows have switched to songs that closely resemble those of rural cousins. Those are the songs all white-crowns sang in our previous world.
No longer competing with our wheels, the birds' songs once again could be the softer, more complex calls nature gave them. They made the change rapidly, the study showed.
The natural songs also doubled the city birds' communication distance, said Elizabeth Derryberry, a behavioral ecologist at the University of Tennessee, Knoxville, and lead author for the study.
Rural birds had no need to adjust their songs.