Pets as Invasive Species: Dogs

May 31, 2023 • by Nicole Elmer

Last in our series on pets as invasive species looks at “Man’s Best Friend.” Are pooches so perfect?

First, let’s define what an invasive species is. We’ve got a great blog on it here, but to summarize: the National Invasive Species Information Center defines an invasive species as non-native to the ecosystem in which it appears. Its introduction causes or is likely to cause economic or environmental harm to people as well as native species. It’s important to note that not all non-native species cause harm and can actually be beneficial. There are many examples but one is the purposely-introduced South American phorids used to control invasive fire ants (Solenopsis invicta). This has been extensively researched at Brackenridge Field Lab.

So then, where does Fido fit into this? Dogs (Canis lupus) are responsible for predation, outcompeting native wildlife for food, interbreeding with other species, and spreading disease. The Global Invasive Species Database states that domestic dogs threaten a total of 200 IUCN Red List species. Thirty of these species are classed as critically endangered, 71 are listed as endangered, and 87 are listed as vulnerable. Dogs have contributed to the extinction of nearly one dozen wild bird and animal species. Feral dog populations or domestic dogs left to roam are the biggest perpetrator of these issues. As such, dogs have become the third worst human-introduced predator after cats and rats. Both feral dogs and domestic dogs can also gather in packs where they corner and kill an animal. I personally have been the unfortunate witness to a pack of four domestic dogs from two different farms corner and kill a sheep, dogs that were otherwise friendly. In a different instance, two loose domesticated dogs also killed a family cat.

Sadly enough, many conservationists say this issue with dogs does not get enough attention, and that many dog owners believe that when their pets roam, either intentionally or accidentally, they do not cause problems. Conservationists note that a firm number on how many dogs are feral or free-roaming is difficult to pin down, although it is understood that the number rises as the global human population rises.

It is believed that domestic dogs diverged from grey wolves about 100,000 years ago. About 15,000 years ago as humans transitioned from nomadic lifestyles into more settled agricultural ones, they began to breed dogs for certain desirable traits: assisting with hunting, herding, pulling loads, serving as guards, and catching rats. Because dogs are so closely associated with humans, they are found everywhere. And much like all of our other pets covered in this blog series, in the wild they cause serious damage.

The biggest threat dogs pose is through the diseases they can carry, like rabies and canine distemper virus (CDV). They were the most likely spreaders of CDV that caused several fatal epidemics within the Serengeti-Mara ecosystem in East Africa. These affected species include silver-backed jackals (Canis mesomelas) and bat-eared foxes (Otocyon megalotis) in 1978, and endangered African wild dogs in 1991 (Lyacon pictus). In 1994, 30% of a Serengeti lion population (Panthera leo) succumbed after contracting morbillivirus, a relative of CDV. It was believed this disease was transmitted from dogs to hyenas and then to these lions. That year, the virus spread later to other hyenas, lions, bat-eared foxes, and leopards in the Maasi Mara National Reserve.

In Israel, feral dogs are a threat to endangered mountain gazelles (Gazella gazella). In Chile, when pudú, the world’s smallest deer, are brought into rehabilitation centers, 70% of their injuries are caused by dogs. In India's state of Rajasthan, there are less than 100 great Indian bustards (Ardeotis nigriceps), an endangered species, and their numbers are threatened by dogs.

Feral dogs aren’t the only cause of ecological damage. Here is an example of the damage a domesticated dog can do when its owners let it roam. In New Zealand during a study of kiwi birds researchers had tagged and tracked, the death of 13 out of 23 birds was on account of one German Shepherd. Further investigation led them to believe that this single dog had killed over 500 birds.

Common sense practices can help slow the damage significantly. Keep your pet on a leash when leaving the house with it. If you allow your dog to be outside, keep it inside secured fences that do not have holes where the dog can escape. Spay or neuter your dog to prevent unwanted puppies. Escaped domestic dogs can mate with feral dogs as well as wild animals like wolves. Always make sure your dog’s shots are up to date, not only for the health of your pooch, but for the well-being of the wildlife it may encounter.

Check out our other blogs on pets as invasive species! Intro blog is here. Then take a look at cats and fish. Not to be outdone are reptiles and amphians and birds.