"There is a very strong correlation between the frequency of wildlife-vehicle collisions and traffic volume. In Estonia, it is clear that most accidents occur on the country's main highways: Tallinn–Tartu, Tallinn–Narva and Tallinn–Pärnu," said Maris Kruuse, a junior research fellow at the University of Tartu. Vehicle speed also plays a role. Since there are no cheetahs in Estonia, local wildlife is not adapted to dealing with cars moving at cheetah-like speeds.

In her doctoral dissertation, which she is set to defend soon, Kruuse examined the temporal dynamics of wildlife-vehicle collisions in Estonia across months, days of the week and times of day. She also studied how the lighter traffic caused by COVID-19 restrictions in various countries during the spring of 2020 affected collision rates. In addition, she assessed how responsibility is assigned in wildlife collisions and how this influences reporting statistics.

"In Estonia, no one is held responsible. If you accidentally hit a wild animal, you do not have to pay a fine, even if it happens in an area marked with a wildlife warning sign," she said.

Lessons transcending species

The first study in Maris Kruuse's doctoral dissertation examined when wildlife-vehicle collisions occur in Estonia.

"We are currently in spring, which is a very dangerous period, as the study also showed. It varies somewhat by species, but generally the peak comes in spring, especially in May and early June," she said.

Many animals have offspring in the spring. Female moose drive away the previous year's calves in May, meaning inexperienced adolescent moose may be more likely to wander onto roads. Likewise, young roe deer that have recently become independent often search for new territories in late spring and early summer.

According to Kruuse, an even more dangerous period is autumn when moose and deer enter the mating season.

"Male animals in particular move around more, tend to lose caution and become overly bold," she said.

Wildlife activity on roads also increases during the hunting season. Driven hunts begin on October 1, causing animals throughout a given area to move more frequently. Wild boars, meanwhile, enter their mating season in autumn and early winter. Darkness and poor road conditions further increase the risk of collisions.

Over the course of a day, wildlife-vehicle collisions occur most often during rush hours when people are commuting to and from work.

"Animals' activity patterns overlap with human movement in the mornings and evenings. That is when the risk of collisions is especially high," Kruuse said.

Many collisions occur shortly before dawn or around sunrise, as well as at and after sunset. Wild boars stood out as an exception, with collisions occurring throughout much of the night due to their nocturnal habits.

The comparison of weekdays also revealed a link between collision numbers and traffic volume.

"Animals do not know whether it is Monday or Wednesday," Kruuse said.

The study nevertheless found that collisions involving roe deer, wild boars and moose occur most frequently on Fridays when traffic is particularly heavy in the afternoon and evening.

Covid spring a respite for wildlife

A second study, a comparative case study of 11 countries, confirmed that when people travel less, wildlife-vehicle collisions also decline. The unique opportunity for road ecology research arose from the COVID-19 restrictions imposed in many countries in the spring of 2020.

According to Maris Kruuse, there was a clear relationship between the severity of restrictions and the number of collisions.

"For example, in neighboring Sweden, restrictions were relatively mild, which was reflected in the fact that neither traffic volumes nor wildlife collisions declined significantly," she said.

In Lithuania, however, collisions shifted more toward urban areas, as reduced human activity encouraged animals to venture more boldly into suburban neighborhoods.

In Estonia, where restrictions were stricter, traffic volumes fell immediately in the spring of 2020, primarily due to a reduction in passenger car traffic rather than freight transport. As restrictions eased, traffic levels began to rise again.

"We compared wildlife-collision figures from that spring with the average for previous springs and found that a significant number of animals survived thanks to the restrictions," Kruuse recalled.

To help wildlife move across increasingly busy highways, various crossing structures have been built. The most visible to motorists are green bridges, or ecoducts.

"Monitoring of the Kolu ecoduct on the Tallinn-Tartu Highway, completed in 2013, suggests that building them is worthwhile," Kruuse said.

Initial monitoring conducted with trail cameras in 2015–2016 and follow-up monitoring in 2020–2022 confirmed that while the crossing was initially used mainly by domestic cats, small mammals and roe deer, larger animals later began using it more frequently as well, including moose, the species for which Estonia's first ecoduct was built.

Estonia's system working

In a separate study, Maris Kruuse also analyzed how responsibility for wildlife-vehicle collisions is assigned in different countries and how this affects reporting rates. In Estonia, no one is held liable when a vehicle collides with a wild animal and drivers are not fined.

"There is no provision holding the driver, the Transport Administration or the local hunting association responsible. To me, the Estonian system seems logical," Kruuse said.

The international comparison showed, however, that in some countries, including Spain, Serbia and Slovenia, hunters can be held responsible for wildlife collisions that occur during the hunting season. In some jurisdictions, drivers are liable if the collision occurs in an area marked with wildlife warning signs. In Hungary and Slovenia, drivers are legally required to compensate hunters for the loss of a game animal, although such cases rarely proceed that far in practice.

Overall, the analysis suggested that when people feel they could be held responsible, they are less likely to report collisions.

"Even in Estonia, not everyone knows that hitting and killing a wild animal does not result in a fine. As a result, some incidents are probably concealed or simply go unreported because people do not know whom to notify," Kruuse said.

Kruuse believes Estonia's official collision data is generally reliable, although the number of unreported incidents remains unknown. Because collisions involving moose are difficult to conceal, their statistics are likely accurate.

"With smaller animals, such as roe deer, I know of cases where the animal is put in the trunk and taken home for a barbecue," she acknowledged.

While the meat does not go to waste in such cases, Kruuse said she would prefer that these incidents also be officially recorded for statistical purposes.

Under Estonian law, large game animals killed in traffic accidents belong to the local hunting association. Keeping the carcass is, in practice, equivalent to poaching, Kruuse noted.

"Smaller animals, however, may be collected and sometimes are," she said.

The remains of small game animals may be taken to feeding sites for eagles, provided to zoology students for dissection or used in taxidermy, jewelry and other projects.

"If a collision occurs, it should always be reported when a large game animal is involved and it would be good to report collisions with smaller animals as well. The state's information hotline is 1247 and they forward the information to the appropriate parties," Kruuse said.

The information is then passed on to the local hunting association, which is responsible for removing the carcass from the road. Hunting associations maintain designated sites where carcasses can be taken to provide food for scavenging animals.

"If a large animal is injured rather than killed, hunters are required to track it down and euthanize it so it does not continue to suffer," Kruuse added.

The removal of smaller animal carcasses from state highways is handled by the Transport Administration through its maintenance partners, while local governments are responsible for local roads.

Drivers can help prevent collisions by avoiding unnecessary trips and by being especially cautious during wildlife activity peaks.

"If you see an animal by the roadside, you should always assume that it may enter the roadway and that it may not be alone," Kruuse said.

Maris Kruuse, a road ecologist and deputy head of the agroecology research group at the Agricultural Research Department of the Estonian Rural Research and Knowledge Center, will defend her doctoral dissertation in geoinformatics, "Factors Influencing the Occurrence and Reporting of Wildlife-Vehicle Collisions and the Performance of Wildlife Crossing Structures as Primary Mitigation Measures," at the University of Tartu on June 8. The dissertation was supervised by Professor Tõnu Oja of the University of Tartu. The opponent will be Senior Researcher Jyrki Pusenius of the Natural Resources Institute Finland.

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