The Value of Volunteers in Global and US State Roadkill Data Collection

Fraser Shilling, Road Ecology Center, University of California, Davis
Topic Area
Partnerships and Collaborative Approaches for Improving Transportation Ecology

Volunteer/citizen science is a quickly evolving field that is receiving attention as a way to mobilize people's involvement in information development, social action, large-scale data gathering, and participation in institutional decision-making. A direct way that most people experience wildlife is through seeing roadkilled animals on the roadside. Volunteer-based roadkill observation systems are springing up all over the US and world and in some places may be the primary source of data about wildlife-vehicle conflict (WVC). I will discuss the role of volunteer-collected WVC data using the global network of similar systems ( We developed the California Roadkill Observation System (CROS) and its companion Maine Audubon Wildlife Road Watch as a way to involve the public in collection of WVC data and as a way to collect large amounts of these data. I present a 10-year assessment of the quality and contribution of these volunteer-collected data to transportation and ecological research. Both systems have collected ~80,000 observations by ~1,500 observers, representing >500 wildlife species. Volunteers were classified as professional biologists or non-professional users, and their rates of species observations and identification accuracy compared. About 20% of the volunteers were professionals, but they provided over 1/3 of the observations, and they observed a more diverse set of species than non-professionals. The diversity index of observations by professionals was similar to non-professionals, and accuracy of species identification was similar for both groups. Locational accuracy for California observations was estimated to be ±14m (n = 552 records). Species identification accuracy rate for observations with photographs was 97% (n = 3,700 records). These data have been to develop hotspots (density and clustering) analyses to inform WVC mitigation planning in CA and ME. The California data has been used to estimate species ranges and compare them to ranges derived from the largest available database of animal observations (Global Biodiversity Information Facility; GBIF). CROS observations expanded GBIF data-derived ranges for 139 of 411 species. In one special case, modeling invasive squirrel (eastern gray squirrel, Sciurus carolinensis) expansion into new areas was improved by adding observations of roadkilled squirrels at the edge of its current range. While non-professional users observe fewer species, their larger number of observations and occurrence over a larger area improves our knowledge of species ranges. Volunteer-collected AVC data from both professional and non-professional users is an underutilized and important data source for augmenting conventional databases of WVC and wildlife observations and range maps. Volunteer systems can and should be used to monitor wildlife occurrences along or near roads and these observations can be used to inform ecological studies and transportation mitigation planning.

Abstract Keywords
citizen science
wildlife-vehicle conflict