Daylight saving time (DST) is often a source of mixed feelings for many people, especially in the United States. While it offers the benefit of longer, sunnier evenings that encourage outdoor activities, the transition disrupts human circadian rhythms, causing sleep loss and related health issues. However, beyond its effects on humans, recent scientific research reveals a surprising benefit of DST for urban wildlife, particularly animals vulnerable to vehicle collisions such as deer and other large mammals.
Each year in the U.S., more than a million vehicle collisions involving deer occur, according to estimates from the Federal Highway Administration. These accidents not only result in the deaths of countless animals but also cause hundreds of human fatalities. Other large mammals like moose and elk also face similar risks. The likelihood of these collisions depends on several factors, including the volume of traffic, animal population density, and the behaviors of both drivers and animals. Tom Langen, a biology professor at Clarkson University who specializes in studying animal-vehicle collisions, explains that DST can play a role in reducing these incidents.
Animal-vehicle collisions tend to spike during specific times such as Fridays, when many people travel for weekend getaways; during full moons, when deer activity increases; and during the fall mating season for deer in North America. The most dangerous time of day is at dusk, when many animals become more active and venture onto or near roads to forage or cross. This is when the highest number of collisions occur. As Langen notes, “The animals get active right after dusk and start moving around, including crossing roads or browsing and grazing along roads, and that’s when they’re hit by vehicles.”
The shift back to standard time in the fall, which moves clocks backward by an hour, inadvertently increases the risk of collisions. This change pushes peak evening commuting hours closer to or even after dusk, when animal activity peaks and visibility drops. A 2021 analysis of over 35,000 deer-vehicle collisions in New York State conducted by Langen and a colleague found that the transition from DST to standard time led to a “far higher” rate of accidents, particularly on workdays. This seasonal clock change effectively increases the overlap between humans’ evening travel and animals’ active periods, raising the chances of deadly encounters.
Supporting these findings, a 2022 study from the University of Washington estimated that permanently adopting daylight saving time could save approximately 33 human lives annually and prevent about 36,000 deer deaths caused by vehicle collisions each year in the U.S. The study also highlighted the potential for reducing the roughly $1 billion in economic costs linked to these crashes, including property damage and medical expenses. Laura Prugh, the study’s senior author and a professor of quantitative wildlife sciences, expressed surprise at one key finding: the increase in collisions after dark during standard time months was not offset by fewer collisions in the morning hours. In fact, the risk of deer collisions was 14 times higher just after dark compared to before sunset, leading to a net increase in accidents during months when standard time is observed.
Interestingly, the springtime switch to DST, which moves clocks forward and results in darker mornings, does not significantly raise the risk of collisions. This is partly because deer tend to be less active in the spring. Additionally, evening commutes during spring DST generally take place before dusk, reducing the likelihood of encountering animals on the road. Thus, while the human experience of DST may vary—with some appreciating longer evenings and others disliking darker mornings—wildlife such as deer clearly benefit from the extended daylight in the evening.
The benefits of permanent DST extend beyond deer to other urban wildlife species that are active during twilight hours. Mammals like raccoons, skunks, and foxes, which often move around near dusk, also face risks from vehicle collisions that could be mitigated by shifting human activity away from peak animal movement times. Even in Australia, studies suggest that koalas could benefit from a permanent switch to DST by reducing their exposure to road hazards during active periods.
Despite the advantages of DST for reducing animal-vehicle collisions, experts emphasize that drivers must remain vigilant year-round. Langen advises motorists to be aware of peak collision times and the tendency of animals to travel in groups, which can increase the danger. Prugh echoes this advice, stressing the importance of heightened awareness around dusk, a time when the risk of animal encounters is especially high.
In conclusion, while daylight saving time often sparks debate among humans due to its mixed effects on