A mountain lion approaching a highway is usually trying to get somewhere: another hunting area, a potential mate, or a territory that isn’t already occupied by a larger, less welcoming cat. These are ordinary parts of a lion’s life, but we have made some of them remarkably difficult.
A new report from the UC Davis Road Ecology Center examines where those journeys end in vehicle collisions, drawing on years of California Highway Patrol records and carcass observations from agencies, researchers, and volunteers. Those accumulated observations reveal stretches of highway where animals are killed again and again. They also give us places to start fixing the problem.
Understanding the Numbers
The report estimates that at least 780 mountain lions die annually on California highways and major paved roads, equivalent to about 18% of the state’s estimated population.
That is a striking number and certainly gets my attention. It also prompts a biologist’s next question: how did they calculate it?
This is a statistical estimate accounting for deaths that go unreported, rather than a count of documented carcasses, and the report provides too little detail to assess its precision. We should be careful with the exact figure.
Nevertheless, independent research tracking radio-collared lions supports the underlying concern that human-caused deaths can reduce overall survival, rather than simply replace deaths that would have occurred from natural causes.
Why Every Population Matters
For a lion population, the consequences depend on who is killed and where.
A breeding female may have kittens waiting for her return; a young lion moving into unfamiliar country may be carrying genes that an isolated population badly needs.
The animal beside the road tells us where one journey ended unsuccessfully, but it doesn’t tell us everything that was lost.
This is why a statewide death toll, however useful, cannot answer every conservation question. A handful of deaths in a small, isolated population may warrant more urgent attention than a larger number elsewhere. We need to understand the populations on both sides of the asphalt.
A Wildlife Crossing Is More Than a Bridge
One of the report’s most useful messages concerns the decidedly less glamorous part of a wildlife crossing project: the fence.
Bridges get ribbon cuttings and headlines, while fencing is often treated as a minor detail. Yet effective, well-maintained fencing is essential to keeping animals off dangerous roadways and, where suitable crossings exist, guiding them toward safer passage.
Existing bridges and drainage structures may also offer opportunities, provided they are suitable for the animals we hope will use them and are maintained accordingly.
For the Mountain Lion Foundation, the lesson is that a wildlife crossing cannot be considered in isolation. We need to protect the habitat leading to it, install and maintain effective fencing, provide safe passage, and monitor whether the project is reducing deaths and restoring movement between populations.
A photograph of a mountain lion using a crossing is encouraging. But the real measure of success is whether more lions survive, reach new habitat, and reproduce.
The goal isn’t simply to help a mountain lion cross a highway. It’s to ensure that the journey continues—and that the populations on either side have a stronger future because of it.
