Road noise may make their songs either inaudible or barely audible, may shorten communication distances, and may even change the perceived location of songs. Extreme or sudden noises flush birds from their nests, not only endangering the eggs but also harming the adults, which use up precious energy in their escape flight. Dutch studies show that road noise may even discourage bird calls in the first place. And these disruptions occur sometimes more than a mile distant from the highway. Other species are at risk too.
Excessive noise causes nausea in some animals.
Kangaroo rats are substantially more vulnerable to predators for several days after being subjected to a loud vehicle, because of the disruption to the rats' hearing. Salmon disappear when the silt, dirt and chemicals brought by roads flow into once-pristine streams. Some calves fail to thrive because road-induced stress inhibits their mother's milk production. Streetlights confuse amphibians and turtles, limiting reproduction. A species' genetic viability may diminish when a road acts as a physical barrier dissecting one population into two, and in extreme cases, roads may cause genetic changes in species, by changing movement patterns.