Animals hit and killed by cars are an unfortunate yet common sight for drivers in California, and anywhere else where animals encounter roads. But UC Davis researchers say there’s a lot we can learn from these fallen creatures.
In 2009, they launched the California Roadkill Observation System. Fraser Shilling, director of the Road Ecology Center at UC Davis, said it’s the largest observation system of its kind in the country.
Since then, he and others have relied on the tool’s data to learn more about the health of animal populations in the state. It’s also allowed him to identify areas where roadkill is more common.
“The Bay Area through Sacramento, through into the foothills and Tahoe, that is where we have the most roadkill in the state,” Shilling said. “The reason for that is we have these big protected areas, big areas of wildlife habitat, right next to mega, urban regions with lots of traffic.”
In the Road Ecology Center’s eighth annual report on roadkill, Shilling and others saw a decline in roadkill reports for mule deer and coyotes. This isn’t necessarily a good thing.
Shilling said that if nothing changes on the road — no increase or decrease in traffic, no measures preventing animals from getting onto the road in the first place — a decline in roadkill could mean a decline in those species’ populations.
Shilling spoke with CapRadio to talk about the history of roadkill research and how this year’s data can guide California’s approach to conserving native species.
This interview has been edited for clarity and length.
Interview highlights
How long have people been tracking roadkill?
People have been looking at roadkill for over 100 years. Some of the first observations and reporting of roadkill were in the 1920s in California, which I think were probably the earliest reports of roadkill anywhere.
The earliest records we could find were collected by [Joseph] Grinnell, who was a well-known biologist who did statewide biodiversity surveys. He just happened to write in his notebook a couple of pages of seeing hundreds of dead animals on the road. This is as he's driving around in a vehicle, a 1920s vehicle, and he speculated at the time that there might be thousands every day being killed on roads in California.
In terms of how we think about it from a wildlife population point of view, there has been recent research suggesting that, if you keep traffic constant, the amount of roadkill is proportional to the size of the wildlife population. There's two things going on there at the same time: Number one, the amount of roadkill is potentially indicating the size of the population. But if you have a lot of roadkill, you're also potentially decreasing the size of that population.
We want to be able to understand both at the same time and that initial measurement of where the roadkill is occurring, what species, when and so on is key to answering those questions.
It seems that there's something we can tell when we see a decline in roadkill of a species and when we see an increase. Can you explain what both of those things mean to you in your research?
It really depends on the type of animal you're looking at. So in the case of deer, we're seeing a decline in roadkill. What that means to us is that, because deer are moving around eating and they're generally staying inside home ranges, the number that are killed is proportional to the number of deer there are total.
So if you see a change in the number of road-killed deer, it means there's a change in the population. And we're seeing a 10% per year decline in the number of road-killed deer. And the most likely explanation is that it's because there's a decline in the population.
Besides the decline in mule deer, we actually saw an increase in the mountain lion and black bear rates of collision. I was wondering about that, and a mountain lion expert and then a non-expert both said the same thing, which was, well, they're moving around more to find food. And if we've got a decline in the deer, and mountain lions prey on deer, that means there's fewer deer for them to find. And a lion moving around more means it's going to cross more roads and they're going to get hit more often.
So the number of deer roadkills going down indicates a decline in the mule deer population. The number of mountain lion roadkills going up indicates that sort of desperate search for food because there’s fewer deer to find.
Is there a way to prevent roadkill from happening?
It goes back to this idea that humans are going to kill some number of wildlife, but wildlife populations can absorb that. Well, that's been debunked. That's not true.
What we're basically causing is an excess death. So you can think of, in the case of deer, anywhere between 5% and 20% of the population of deer in California are being killed by vehicles every year. Every year we have that level of excess death. And at the same time, we're having a decline in the deer population that's similar to that, which suggests that vehicles [are] causing this decline in mule deer populations.
That immediately gives you a place you can go and act. Where can you act? You can act on the roadway. If you fence roads where this is occurring, then you're going to prevent those deaths. You're also going to prevent the death of the people that hit the deer at very high speeds or their injury and the damage to their vehicle. So there's a lot of benefits to that.
What is the state doing to combat this issue?
It has been one of those things where you pound your head against the wall and then suddenly there's some change. The last year, the legislature approved about $1 billion of new funds to plan for wildlife crossings and fencing throughout the state and that is critical. What we need now is [a] requirement that the state collects data about where these wildlife are getting killed, not rely on our volunteer system, and then have a requirement that those data are used to fix the problem. We're missing those pieces.
We've never had funding for our system in the last 14 years and most of the people collecting the data, including the agency staff and scientists, are not getting paid to do that. Nobody's getting paid, and [the data] goes into this system that we maintain as a volunteer benefit to the state. That's not a great way to run wildlife protection in the state, and I think California can do better.
How is this information collected? Can anyone pitch in?
The data that we're collecting now is both from regular people, so to speak, volunteers who collect observations, but also scientists, nonprofit groups, Caltrans maintenance activities, California Highway Patrol.
If you go to wildlifecrossing.net … It's a web app you can use on a smartphone. And basically, if you have your location on in your phone and you take a picture [of roadkill you see], you can press one button and upload that picture and it's geolocated, meaning that you would know exactly where it is. You can add the species if you want, or you can just leave that blank and we'll do it. So it's a very easy process of collecting the data.
There are organizations throughout the state that use our data to plan for how to reduce road kill and improve connectivity. So please go and collect those data. It's critically important to our conservation of wildlife in California.