Image Credit: Clément Bardot, CC BY-SA 4.0, Image Cropped

Ungulates and trains – factors influencing flight responses and detectability (2022) Bhardwaj et al., Journal of Environmental Management, https://doi.org/10.1016/j.jenvman.2022.114992

The Crux

Trains are one of the most climate-friendly ways to cross long-distances. Whether it’s people heading off on holiday or transporting food, clothing or other goods, it’s a (usually) cheap and low-emissions method of travel.

Yet train-animal collisions can be a massive problem for wildlife. Deer in Europe, bears in North America, and elephants in India are three of the many, many groups of species that suffer mortalities every year when they’re hit by trains. The collisions aren’t exactly friendly to the trains either, with many drivers suffering from trauma and repairs often need to be made (granted, not as bad as being run over).

Understanding more about animal behaviour in the face of a train can help us figure out how to prevent these collisions. Today’s authors enlisted the help of Swedish train drivers in an attempt to understand how animals behave when confronted with an oncoming mass of metal.

What They Did

The team distributed dashboard cameras to 24 train drivers across Sweden, where each year around 5000 animals collide with trains. The cameras recorded continuously, and drivers could prompt the cameras to save footage when they detected an animal on or near the tracks during the trip.

The researchers then tested whether the animals elected to flee from the train, which direction they fled in, and how far away the train was when the animals fled. They then compared these factors to where the animals were standing, how fast the train was moving, the time of day, and whether the driver sounded the horn upon seeing the animals.

Did You Know: The Problem With Fences

With all these discussions of keeping animals off the tracks, you might be asking why we don’t just put a fence up. There’s two main reasons, a) they’re expensive to maintain and b) you then run into the issue of habitat fragmentation. Many larger species need large home ranges, as well as the ability to find each other come mating season. Train tracks may represent a threat, but they’re also relatively easy to cross compared to a fence. So by putting up fences, you can cut an individual off from much of its range, and potentially fragment a population, which could do more damage in the long run.

What They Found

The research turned up just under 400 videos featuring just over 600 animals. About 80% of the animals were roe deer. Both roe deer and moose were more likely to flee from trains, though roe deer showed a reduced tendency to flee if they were outside the railway corridor (more than ten metres from the tracks). Light conditions and the time of day didn’t seem to influence their likelihood of fleeing at all.

Interestingly, if roe deer were on the tracks or within the railway corridor, they were likely to initially flee from the train along the tracks, as opposed to getting the hell away from the tracks. If they were outside of the corridor, they tended to flee away from the tracks. Regardless of their position, the use of a warning horn actually increased the likelihood of the deer to flee onto the tracks. Despite this, the use of a horn reduced the likelihood of a collision.

Problems?

This study presents an interesting dilemma. 24 train drivers helped out in this study, and it was by no means mandatory to do so. If they’re more likely to volunteer to help out for an environmental cause, are they more likely to sound horns, or look out for and record wildlife? If so, perhaps they’re not representative of the average Swedish train driver? It’s difficult to know.

So What?

The fact that time of day and light conditions, plus the fact that horns prompted responses from the animals, indicate that it’s sound and vibrations, not the sight of a train, which cause deer to flee. As such, enabling earlier detection (for both the animal and the driver) could reduce the likelihood of a collision. This could be achieved through maintaining a clearer area closer to the tracks, or enabling drivers to detect animals earlier using thermal detection.

The most interesting result was probably that deer chose to flee onto the tracks when danger approached. As my former supervisor Dr. Ivar Herfindal put it, this could simply be a result of the tracks being the most obvious clear escape route.

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Dr. Sam Perrin is a freshwater ecologist who completed his PhD at the Norwegian University of Science and Technology who can’t decide whether deer evading a train by fleeing onto the tracks is tragic or hilarious. You can read more about his research and the rest of the Ecology for the Masses writers here, see more of his work at Ecology for the Masses here, or follow him on Twitter here.