Summary: Brown & Brown (2013)

Erickson et al. (2005) estimate that 80 million birds in the U.S. are killed annually by vehicles. Over a 30 year period, Brown & Brown (2013) found that there was a sharp decline in the incidence of road-kill in cliff swallows Petrochelidon pyrrhonota. Individuals cliff swallows that were killed on roads had longer wings than the average seen in the overall population. Longer wings could mean lower wing loading and inhibition of vertical take-off, resulting in these birds experiencing increased mortality. Alternatively, birds could be learning to avoid vehicles. Brown & Brown (2013) suggest that road mortality could be driving species response to change and could also exert selection for traits minimising collision.