One of the perennial gripes for some hikers is off-leash dogs on the trail. It’s bad for wildlife, they say. Others say it’s not a big deal.
So, what do we know about off-leash dogs and their effect on wildlife? It turns out it can be surprisingly difficult to pin down specifics, but experts tend to agree on some overall points.
Dogs Attacking Wildlife
In general, it does seem to be true that pet dogs can pose a threat to wild animals.
For starters, such dogs have been linked to attacks on tortoises, bighorn sheep and seals resting or foraging on beaches. Even if they don’t catch what they’re chasing, they can amplify stress for wildlife.
“Some dog owners will characterize that as, ‘oh they're just having a bit of fun,’” says Mike Weston, a conservation biologist at Deakin University in Australia. “But, if we can put ourselves in the wild animal’s perspective […] if it doesn't mount an effective escape, it's probably dead or injured, right?”
Experts also say it’s common to hear about even well-trained dogs suddenly and unexpectedly taking off after an animal. Dog poop can also spread diseases or parasites.
Even if a dog is not directly injuring or making wildlife sick, it turns out just their presence — the sound of barking, and their scent, for example — can affect wildlife.
Pet Dogs Elevating Wildlife Stress
In 2008 a group of researchers showed that mule deer, squirrels, rabbits and prairie dogs all stayed away from trails in areas where dogs were allowed. Other studies have found that the presence of dogs can raise stress levels in wild animals.
This can pose problems, since stressed-out animals may have trouble finding food or breeding and raising young. That’s especially concerning if the population of that species is already struggling.
“A lot of species are severely limited by the amount of habitat that they have available to them. So if we're taking out chunks of it and making it less suitable, that can be a big deal for a population,” says Courtney Larson, a U.S.-based conservation scientist at The Nature Conservancy who studies how recreation and conservation can sometimes conflict.
Weston, in Australia, has also seen how recreation can carve up a habitat.
Some Australian beaches are home to the nesting grounds of a dainty little shorebird known as the hooded plover. Authorities would like to protect the plovers, but it’s often put them at loggerheads with local dog-walkers.
Dogs can scare and even kill the birds. In 2019, Weston and his colleagues did a study that included using GPS trackers to see how much of a beach a dog would range about on.
“The amount of beach left for animals that wasn't near a dog was very, very small,” says Weston.
Of course, the specific impacts may differ quite a bit from place to place, since not all animals may react the same way. A deer, a coyote and a bird may all respond differently to nearby dogs, says Larson.
That said, there may be good reasons why conservation authorities try to limit the presence and impact of dogs in a given area.
Leashed vs. Unleashed Dog Impact
Still, questions linger about how much worse off-leash dogs are than leashed dogs in nature. That has been trickier to measure with hard science.
Few studies exist on the subject, and those that have been done present mixed conclusions. Some studies have suggested that unleashed dogs are especially impactful while others found that dogs tend to not stray that far from their humans when off-leash.
Funnily enough, part of the reason for this dearth of data may be due to people taking dogs off-leash in the first place. In many areas, a high number of people ignore leashing regulations, which can make it hard for researchers to find what you might call “clean” data sets to compare against each other.
Unfortunately for dog-walkers, this lack of compliance may end up coming back to bite them, warns Weston. That’s because the alternative to a “leash-only” regulation may be “no-dogs-at-all” regulation.
Weston points to one park in Australia where, after some 20 years of trying to reign-in off-leash dogs, the powers that be eventually banned dogs altogether.
“I would regard that as a bad outcome for all parties, including dog walkers and particularly responsible dog owners who were actually leashing,” Weston says.
Other Reasons to Leash Your Dog
Dog owners may want to keep dogs on-leash for other reasons as well.
While many animals may see dogs as predators, there are some that might see them as prey. This can include black bears, mountain lions and coyotes — or even human hunters that mistake a pet dog for an animal they are pursuing.
Some public lands allow hunters to put down animal traps that might ensnare a dog. And dogs can potentially get injured or sick from things like running into cars or drinking polluted water.
Many parks may also want to keep dogs from certain areas due to construction, fragile plant life (even in deserts) or restoration projects. Some people on the trail may fear or be allergic to dogs as well.
Ultimately, experts recommended that folks looking to go out with their dogs look up and know the regulations ahead of time and follow them. Some places will happily allow dogs to roam free. Others may not.
“While there are many national parks for people and pups to explore, it is important for visitors to check that they can bring their dog with them on their adventure,” says Cynthia Hernandez, spokesperson for the U.S. National Parks Service, who also pointed to an online map of national parks that allow pets.
In the end, we need more data on the effects of letting a dog off-leash and there may be places where it’s okay. But there are also many good reasons to keep them by your side on a hike. “We should err on the side of caution,” says Larson.