Counting Roadkill: A unique tool to assess the movement of mammals in urban areas

Every Friday morning my alarm goes off at 4:15 am. I get up grab a mug of coffee and jump into the truck. The goal: get to the field site before the sun does. The task: to survey and count animals that have been struck by cars (yes we get up this early to count roadkill). Although this might sound morbid and not typically a task that a biologist would do, it has been part of our weekly routine since beginning of 2018.

It is critical to get there before sunrise because we are interested in nocturnal mammals. If they have been struck by cars in the middle of the night, we can count them before they are taken or moved by other scavengers (crows, ravens, etc.).  

This study is directly related to another study that we have been conducting since 2015, assessing the movement of San Bernardino kangaroo rats (SBKR) and other small mammals through culvert crossings in the same area. These culverts are underground tunnels for the passage of wildlife. Instead of animals using the busy road to cross to neighboring habitat, they can pass safely under the road. So far the culverts have been extremely successful in aiding movement for small mammals, birds, lizards and even snakes.

As you could guess we are extremely interested in the movement patterns of small mammals and how they navigate habitat that has been fragmented by roads.

Although I joke that this task seems odd and unusual, the data that we are getting from this study will help us better understand the impact of wildlife vehicle collisions in the remaining areas that have suitable habitat. Understanding the impacts of roads and vehicle collisions is especially important when you are working with a species like SBKR. They have lost over 90% of their habitat to development and the remainder of the areas that they can exist in is separated by roads resulting in a loss of habitat connectivity.

We have six sites where we conduct our surveys. The first portion of our study is a sunrise driving survey. We have a driver and a spotter that takes written notes. To locate roadkill accurately we drive slowly to make sure we can spot even the smallest amount of animal carcass. When roadkill is spotted we stop the truck, identify the animal (if it’s not too squished), take a picture and a GPS point so we know its exact location. So far we have counted desert cottontails, a gopher, a woodrat, a California King snake, and a few songbirds that we were unable to identify down to species.

The second portion of our study is using remote game cameras on the side of the roads to take pictures of roadkill events when we are not there. We have two cameras on each site that are secured and locked to street signs, fences, and light poles to give us the best vantage points of the roads. The cameras are set to take pictures of movement throughout the night. Although the majority of the pictures are cars passing by, we have seen several animals using the roads such as deer, coyotes, raccoons, and rabbits. Capturing the pictures of the deer was especially exciting because we did not know they were in that particular area.

Studying the impacts of wildlife vehicle collisions can have several implications. In areas where the amount of collisions is high wildlife crossings such as culverts or bridges can be built. Other options may include fences that help keep wildlife off the roads, but that’s when a crossing needs to be installed so animals can still cross from habitat to the next.

On a larger scale, wildlife vehicle collisions can cost the state of California more $250 million a year! They also result in terrible human injuries and sometimes even death. Drivers are actively trying to avoid animals that are crossing the road but end up putting themselves in extreme danger. This is even more of an incentive to study the effects of these accidents involving wildlife so as biologists we can give our input on how to solve this complex problem.

We plan on continuing surveying for roadkill through the end of August and we will continue to study the effectiveness of the culvert crossing through the next few years.

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