Why did the bird not cross the road? Noise, it seems, forms at least part of the explanation.

Credit: CONRAD TAN/FLICKR OPEN/GETTY

Christopher McClure, Jesse Barber and their colleagues at Boise State University in Idaho created a 'phantom road' to test the effects of traffic noise without any actual cars or disruptions in the visual landscape.

The authors played continuous traffic sounds through speakers spaced evenly along a 0.5-kilometre ridge for four days, followed by four days of silence. They monitored multiple sites along the fake road and in a control area every morning for 7.5 weeks.

When recordings played, the number of birds along the road declined by more than one-quarter. Two species, the cedar waxwing (Bombycilla cedrorum; pictured) and yellow warbler (Setophaga petechia), avoided the noisy road almost completely.

Proc. R. Soc. B 280, 20132290 (2013)