The rapidly expanding road network threatens the persistence of many terrestrial species through mortality associated with wildlife-vehicle collisions. Roadkill monitoring under-estimate actual collision numbers as the time during which roadkill carcasses remain visible on the road is often shorter than the frequency of road monitoring. By placing passerine and amphibian carcasses on stretches of roads we surveyed every 2 h, we fine-tuned existing persistence estimates for these species. The time for half of the carcasses to disappear was less than 30 min for birds and 1–18 h for amphibians depending on the volume of traffic, which is much shorter than previous esti- mates. We show the implications of our results by performing roadkill surveys on common toads 3 h after the window of reproductive migration, showing roadkill is under-estimated by half, and by estimating from citizen-science data that passerine collisions could be as high as 10 in- dividuals.km-2.year-1 in south-eastern France.