The amount of noise in an area affects the number of songbirds seen in that territory. Two studies from two different parts of the world show the same thing: birds don’t like noise. Although some species can be tolerant of noise, increased background noise levels lead to decreased diversity.
The first study took place in Puebla-Cholula, Mexico, and was run by scientists from the University of the Americas and from the Basque Institute for Agricultural Research and Development. The second study, conducted by researchers from the University of Extremadura, Spain, took place in the Iberian Peninsula. In both cases, the number of bird species in an area was adversely affected by the amount of background noise. In fact, noise levels were a greater predictor of species diversity than was size of test area, or human usage. For example, university campuses had many more species of songbird than urban parks.
The Spanish study suggested that the cut off for discouraging the more sensitive bird species was 50 decibels (dB). That’s about as loud as a normal conversation in a quiet location. A whisper is at about 30 dB and traffic sounds heard from inside your car are around 85 dB. All the regions studied had at least 38 dB of background noise, and some had over 70 dB.
What can be done to encourage birds to live alongside people? The authors of both studies propose that urban planners include acoustic barriers, such as wooded spaces, within city limits.