Using Roadkill as a Lens to Understand Animal Movement and Mortality

General Introduction

The study took places within the Oak Openings Region, a biodiversity hotspot in northwest Ohio. The Oak Openings was created during the Cenozoic period, a time where glaciers continuously moved across Ohio, creating valleys and riverbeds. When the Wisconsin glaciers melted back from Ohio around 14,000 years ago, waters were released into multiple lakes with sandy beaches. Overtime, these sandy beaches started to become dunes characterized by rain water that could not drain past the clayey till and bedrock ground later. Water that would stand between the clay layer and sandy dunes provided moisture to support oak savanna habitat. Between the sand ridges, rain water would saturate the land, which created open areas of wet prairie. The combination of oak savanna habitat and open wet prairie gave this region the name of “Oak Openings”.

Today, the Oak Openings looks quite different as a result of the economic development and agricultural pursuits along the Toledo-Detroit corridor. This area is highly fragmented by roads, agricultural fields and urban/residential development. Roughly 45% of the Oak Openings Region contains urban and suburban development and roughly a quarter of the region has been converted to areas of agricultural production. However, there are still remnants of wild lands that exist west and south of the city of Toledo. This area is Ohio’s largest single surficial sand covering which is 1-12 meters thick and consists of wet lowland and sand ridge terrain with elevations up to 210 meters above sea level. This area is approximately 8 kilometers wide and 32 kilometers long and contains oak savanna, oak woodland and wet prairie habitats on post glacial beach ridges and swales that covers 345 km2.

The Oak Openings Region contains one third of all of Ohio’s endangered plant communities as well as many rare animals and early successional ecosystems. However, only about 10% of the Oak Openings Region is in protected areas (Abella et al., 2007). Early successional ecosystems in this area (e.g. oak savannas and prairies) were historically disturbed by fire. Now, these disturbances are mimicked by management activities such as prescribed fires and thinning. In Ohio there are two preserve known as the Oak Openings Preserve and Maumee State Forest. These two preserve are the largest protected areas and contain many different vertebrate populations and species. However, these two preserve are highly fragmented by agricultural fields, roadways, railways, and trails that may limit animal movement and increase road mortality. Therefore, it is critical to better understand animal movement and road mortality in this area to promote viable populations, increase our knowledge of vertebrate movement and prevent the killing of vertebrate species by vehicle collisions.

Abstract

In the United States, road networks are vast and most effects of roads on native species are negative. Roads can reduce population connectivity or structural features along roadways can affect vertebrate movements by acting as barriers, attractants or a source of mortality. In order to reduce negative impacts of roads, it is important to understand how structural features (e.g. vegetation density, canopy cover, road features, and land cover types) spatial factors (e.g. traffic density, speed) and environmental variables (e.g. temperature, humidity, and rain) relate to animal life history, road mortality and movement across vertebrate taxa (e.g. amphibians, reptiles, birds and mammals). This study uses roadkill as a lens to study animal movement and identify structural features of roads that may be managed to reduce road mortality. In the Oak Openings Region, a biodiversity hotspot in Northwest Ohio, May-October, we surveyed roads surrounding and within Oak Openings Preserve and Maumee State Forest, the largest protected areas, for all vertebrate taxa. We also performed daytime and nighttime surveys within the parks to account for sources of animal dispersal and dispersal corridors. We found 292 vertebrates dead on roads surrounding protected areas, including more mammals than any other taxa. Almost 44% of road mortality was found on one roadway that appears to be an area of frequent vertebrate crossings and mortality from vehicle collisions and animal movement in visual surveys was primarily in the NW and SW area of the Oak Openings preserve, adjacent to that road. Intermediate levels or no canopy on roads increased the number of road killed vertebrates for all surveyed months (Wilcoxon, p<0.02). Road structural features influenced vertebrate road mortality, but the effects varied among species and months. Specifically, the presence of agriculture fields, vertical road signs, grassy fields, verge slope, forests and water influenced vertebrate road morality (Chi-Square, p<0.05). Land cover types along the roads and edges influenced animal movement and road mortality for mammals and birds during all surveyed months (Chi-Squared, p<0.05). Our approach predicted animal movement and idnetified the features that may be managed to reduce road mortality, which is likely to be applicable to other reserves in human-dominated landscapes.