These are all possibilities and experiments need to be carefully set up to test each factor. Researchers at Boise State University have conducted a new study designed to eliminate all factors except traffic noise to see what effect it has.
|Researchers created a virtual road to simulate traffic noise in a roadless area.|
Post doctorial research associate Christopher J.W. McClure said, "We present the first study to experimentally apply traffic noise to a roadless area at a landscape scale, thus avoiding the other confounding aspects of roads present in past studies."
The researchers alternated periods of playing and not playing noise during fall migration and used bird surveys to document differences in bird presence during those times.
“We documented more than a one-quarter decline in bird abundance and almost complete avoidance by some species between noise-on and noise-off periods along the phantom road,” said Jesse R. Barber, assistant professor of biological sciences.
Could this have been a fluke or coincidence? As birders know, migration can be hit or miss. Luckily, the researchers also included control sites in their experiment. Barber states, "There were no such effects at control sites. This suggests that traffic noise is a major driver of the effects of roads on populations of animals.”
In science we need to be careful about drawing conclusions. The researchers say traffic noise is a major driver but this does not mean we can exclude other factors. We need more experiments like this, that only test one variable at a time, to truly understand the big picture of how roads impact birds. What we can say, based on this data, is that traffic noise should be strongly considered by land use managers as they think about bird populations.
“An experimental investigation into the effects of traffic noise on distributions of birds: avoiding the phantom road,” 10.1098/rspb.2013.2290 published in the Proceedings of the Royal Society
This article was based on information in a press release from Boise State University.
Photos courtesy of Boise State University.