Daily roadkill monitoring and long-term population census reveal female-biased mortality for a small mammal along a wildland-urban interface

Expanding road networks in the wildland-urban interface may increase wildlife mortality from vehicle collisions. However, our knowledge of long-term roadkill rates and impacts on vertebrate populations is poor. We capitalized on a 31-year study to determine how roadkill rates varied with demography and traffic volume in a population of golden-mantled ground squirrels (Callospermophilus lateralis; GMGS) along 1 km of rural road in Colorado, USA. Despite low annual numbers of roadkill events (0–7 GMGS), adult female mortality was high (10.9 %) and increased with female cohort size. Adult roadkill rates increased with our traffic volume index. We estimate 71 % of roadkill events would have been undetected if we performed weekly instead of daily surveys. Hence, population-level impacts of road mortalities are likely underestimated in short-term studies that lack paired demographic data. Understanding true rates of roadkill in wildland and developing areas will help inform conservation strategies.