Most folks that enjoy listening to birds realize that noise created by traffic, machines and other manmade sources affects our ability to hear birds. However, we have little understanding as to just how much these sounds impact our ability to hear the songs and calls of songbirds.
However, the recent Covid-19 pandemic provided researchers with the opportunity to study this situation. During those trying times, we were living through shutdowns that kept many Americans off the highways and homebound, consequently manmade noise levels were down. As a result, many of us noticed that the outside world seemed to be a quieter place. Fortunately, some during this time researchers were hard a work measuring these sound levels, and their impacts on birds and those of us that enjoy hearing them.
Nancy Lawson noted in her excellent book Wildscape that one of the findings David Luther and his colleagues at George Mason University made was that noise levels dropped in some locales in the San Francisco area to those typical of the 1950s. This enabled folks to hear four times more birds than they could prior to the pandemic. In addition, some species could actually be heard twice as far away.
This is a classic example how humans are affecting our world.