Human roads have utterly fragmented the world of wild animals but the engineering to reconnect the pieces is in our grasp
Darryl Jones is professor emeritus of ecology at Griffith University in Queensland, Australia. His books include The Birds at My Table: Why We Feed Wild Birds and Why It Matters (2018) and A Clouded Leopard in the Middle of the Road New Thinking about Roads, People, and Wildlife (forthcoming in 2022). He lives in Brisbane.
It is almost certain that you recently interacted closely with an invisible giant, as the Harvard landscape ecologist Richard T T Forman has described it. Others have called roads ‘the single most destructive element in the process of habitat fragmentation’, declaring that ‘Few forces have been more influential in modifying the Earth than transportation.’ Yet you probably didn’t even notice. An expansive feature that snaps the globe but is effectively invisible: the vast network of transportation infrastructure – all the railways, canals but also, most significantly, roads. Roads are everywhere, forming an almost inconceivably complex system, an endless, ever-expanding, interconnected grid that facilitates the movement and exchange of people and goods over vast areas. This colossal structure is probably the greatest ever cultural artefact, a requirement and precondition for human development. For us, roads are essential connectors, linking places and purpose. But almost everywhere these networks have been imposed with scant regard for the landscape in which they occur.
Despite its extraordinary scale, this vast, inescapable, indispensable network is largely ignored. As we hurtle between the places where we live, shop, learn and play, the road on which we travel is unlikely to cross our minds. (The traffic we encounter is, of course, another matter.) We are even less likely to conceive of the road on which we are travelling as a component of the huge, sprawling web made up of all the roads spreading out over regions and the entire continent.
If we conceive of a road at all, it is most likely as a trip taking the shortest distance from A to B as displayed by a map app on a smartphone. Much harder to envision is the network of interconnected roads, a literal web, sometimes densely meshed in places where many people live, sometimes in diffuse bands that skirt around areas of difficult terrain where human presence is low. It is not only the most efficient connection for people we should consider, of course, but also the resulting subdivision of the landscape into pieces – fragments – of land bounded on all sides by roads. These pieces may be city blocks, farms or national parks but they are all, to some extent, circumscribed by the surrounding roads and the traffic these carry. Unsurprisingly, there are strong and obvious relationships between the density of humans and the density of roads. This is most evident in small countries with large populations. The Netherlands, for instance, compact and crowded, has a road density of 1.55 km (0.96 miles) of road per square kilometre. However, even in a country as apparently spacious as the continental United States, there is almost nowhere more than a few miles from a paved road.
Why might this matter? Imagine any large animal, a deer or wolf perhaps, that needs to travel for any typical but compelling reason: finding food, seeking a mate, regular migration. Wherever it lives, wherever it moves, sooner or later it will come upon a road. What happens next will depend on a lot of different factors. It may travel this route regularly and be quite familiar with the abrupt change in the landscape. Or it may have never encountered a road before. It may even be attracted to the roadside to graze on the grass, sample the edible trash or scavenge the dead animals found alongside. On the other hand, the noise or lights of the traffic may be so disturbing that the animal retreats as far away as possible. The animal may cross if there are no vehicles, or inexplicably wander straight into the traffic. It may be sufficiently motivated to cross despite the risk or, having learned to judge what are safe intervals between moving vehicles, it may delay crossing until the quietest parts of the night. All of these responses are happening almost everywhere every day.
Crossing a road with traffic is often dangerous for wildlife, especially for slower, ground-dwellers. Collisions with vehicles almost always lead to the death or serious injury of the animal, and the numbers involved are almost unbelievable. For example, about a million individuals of all species are killed every day on the roads of the US…