What Bear Hair Reveals About a Highway Bridge

A bridge covered with soil and shrubs may seem like an unusual way to cross a highway. In Canada's Banff National Park, however, planted bridges help wildlife travel over the busy Trans-Canada Highway. The road divides animal habitat, the places where animals find food, shelter, and mates. Roads can become barriers that leave groups of animals isolated, or separated from one another. Wildlife crossings offer a way to reconnect those groups.

A Route Above Traffic

An overpass carries animals above traffic, while an underpass provides a route beneath it. Banff uses both kinds of crossings. Long fences beside the highway help guide animals toward their entrances. This matters because a bridge cannot help an animal that approaches the road far from the bridge and does not find it. The fences and crossing structures work as a system, rather than as separate projects.

A photograph of a Banff overpass shows a planted strip stretching above the highway lanes. A useful caption would be, "Plants cover a wildlife route above moving traffic." Such a photograph helps explain the design. However, the picture alone cannot show whether animals actually use the route or whether it connects groups over many generations.

Evidence Caught on Hair

Researchers can use cameras to record animals entering crossings. They can also collect hair left on special sampling wires. A small hair sample can provide DNA, the material that carries inherited instructions. Using genetic information, scientists can distinguish one bear from another instead of counting every visit as a different animal. Samples gathered elsewhere in the park help researchers compare bears using crossings with bears living in the surrounding area.

Genetic research in Banff found that some black bears and grizzly bears that used wildlife crossings also produced offspring. Researchers also found evidence of breeding connections between bears on opposite sides of the highway. These results support a stronger point than a camera image does: crossings can help animals exchange genes between separated groups. A photograph records a trip; genetic evidence can reveal connections reaching into the next generation.

What the Evidence Cannot Promise

These findings support wildlife crossings, but they do not prove that any bridge in any location will work equally well. The Banff research involved a system containing both overpasses and underpasses. Its results should not be presented as proof that planted bridges alone caused every benefit. Animals differ in which structures they use, and the location of a crossing matters. A successful design needs to fit the animals and the landscape around it.

Continued monitoring, or repeated checking, helps test that fit. Cameras can show which species visit and whether use changes over time. DNA can help reveal which individuals cross and whether breeding connections develop. If cameras record few visits, researchers may need to investigate the location or the approaches. Each kind of evidence answers a different question, so combining them gives planners a more complete picture.

The strongest case for a wildlife bridge is not simply that it looks green. It is that animals find it, use it, and maintain connections across a busy road. Banff's bear research shows why evidence matters: a few strands of hair can help test whether a crossing is doing a job that a photograph cannot fully reveal.