Wild deer release millions of metric tons of methane into the atmosphere every year, making them the largest source of the greenhouse gas among wild ruminants, according to a new analysis by researchers at the Max Planck Institute for Biogeochemistry in Jena, Germany.
The study, led by Theresia Yazbeck, set out to compare the digestive gases released by wild animals with those produced by domesticated livestock. When cows belch and fart, they emit methane, a potent greenhouse gas that has been rising rapidly in recent years. Wild ruminants such as deer, moose and llamas rely on the same biological process: bacteria in their guts help them break down fibrous plants, and the digestion produces methane as a by-product.
To estimate how much methane wild ruminants release, Yazbeck and her colleagues used recent estimates of global wild animal populations and combined them with methane emission estimates based on body mass and diet. That approach allowed the team to assess emissions across a broad range of species rather than relying on measurements from a small number of animals. The results show that deer add the greatest amount of methane to the atmosphere of any wild ruminant.
Even so, the total contribution of deer and other wild ruminants is minuscule compared with domesticated livestock. Cows and other farm animals produce methane through the same digestive mechanism, but the overall scale of livestock production makes domesticated animals the dominant source of animal-related methane.
The finding helps address a longstanding challenge in climate science: methane has been accumulating in the atmosphere quickly, but researchers have found it hard to pin down exactly where the gas is coming from. Some releases are tied to human activity, while others come from natural sources such as wildlife. By quantifying the wild-deer share, the team has added a more detailed piece to the global methane picture.
Methane is a potent greenhouse gas, and its concentration in the atmosphere has been rising rapidly in recent years. Knowing how much comes from wild animals is important for building a complete count of all sources. The new estimate gives scientists a clearer baseline for the natural side of the methane cycle and a better basis for comparing wild emissions with those from farming.
The study does not change the larger picture for climate accounting: compared with livestock, wild deer are a minor source of methane. But the research highlights that even familiar woodland animals are part of the planet's methane cycle, and their emissions can now be counted with greater confidence.
