Fido, Fluffy, and Wildlife Conservation: The Impact of Pets on the Environment

September 27, 2017

Domesticated cats and dogs are intertwined with modern society influencing both their owners and the environment. Researchers from Carleton University have published a new paper in Environmental Reviews on the diverse impacts these animals can have on wildlife.

By: William Twardek, Kathryn Peiman, Austin Gallagher, and Steven Cooke

Domestic relationships among humans and wild animals extend back to the last Ice Age with the wolf and wildcat—among the earliest animals domesticated by humans—becoming the cuddly companions we see today. Our relationship with dogs and cats has permeated human culture for thousands of years, with current estimates suggesting that the dog was domesticated over 15,000 years ago and the cat 9,500 years ago

Today these animals can be found in almost every human society around the globe with an estimated 500987 million dogs and up to 752 million cats. This suggests there is approximately 1 domestic cat or dog for every 58 people on earth. The sheer abundance of these animals creates the potential to influence not only humans but also the environment and animals these pets interact with. 

Domestic dogs can capture prey up to 4 kg in size, while cats may kill prey for "fun". The impacts of our fluffy friends on wildlife are wide ranging and are often overlooked by pet owners. In our new review, we explore the diverse effects these animals can have on the conservation of wildlife and suggest tips for pet owners to follow to improve the harmony between our pets and wild animals.

Cuddly killers

Predation by cats and dogs is considered one of the primary threats to wild birds and mammals. In the United States alone it is estimated that cats capture and kill between 1.31.4 billion birds and 6.322.3 billion mammals a year, and up to 350 million birds annually in Canada. Some of the most severe problems, however, occur on islands where prey species may not have natural predators making them naïve to cats and dogs and particularly vulnerable to population declines. 

Differences in feeding exist between dogs and cats. Dogs are social and typically take a few large meals, while cats are solitary and take many small meals. Differences in hunting behaviour can also vary substantially between individual pets, with some individuals capturing no prey at all while a few individuals are responsible for the majority of prey. Worldwide, cats on islands have been recorded to consume roughly 250 animal species and were a major driver of extinction for 33 species. This number comprises 14% of modern global mammal, bird, and reptile extinctions. The impact of cats is epitomized by the tale of the lighthouse keeper.

Although somewhat controversial, the tale claims a single cat named Tibbles owned by the lighthouse keeper on Stephens Island, New Zealand, was entirely responsible for the extinction of a flightless bird, the Lyall’s wren (Traversia lyalli). Free-ranging dogs can have similar effects on islands. Dogs were strongly implicated in the extirpation of rock iguanas (Cyclura carinata) on the Caicos Islands, the Conga hutia (Capromys pilorides) in Cuba, and marine iguanas (Amblyrhynchus cristatus) in the Galápagos.

Although the population effects of successful predation leading to death are relatively well known, the impacts of partial or unsuccessful hunting attempts are underappreciated. Up to 68% of hunting attempts are unsuccessful, and include cats playing with prey and dogs harassing wildlife, leading to behavioural changes and physiological stress in the prey. Injured prey may escape or be left behind but die later, and few are likely brought in to veterinarians or rehabilitation centers. As a result, we may be underestimating the total number of deaths caused by domesticated animals.

But pets aren’t all bad

The strong relationship owners have with their pets can influence people’s beliefs and attitudes towards wildlife. Ownership of a pet can increase the time people spend in nature which corresponds to decreased fear of wild animals, as well as greater understanding, appreciation, and connectedness towards nature. Overall, positive attitudes towards nature increase the likelihood that pet owners will engage in environmentally respectful behaviours and will be concerned about environmental issues. Additionally, pets can play important roles in conservation. For example, wildlife detection dogs are highly efficient at identifying endangered species that are rare or difficult to identify using human surveys.

Is my pet to blame?

The impact that cats and dogs have on the environment largely depends on the extent to which they are allowed outdoors, which is generally under control of the human owner. While virtually all owned dogs go outside to relieve themselves, many owned cats are restricted entirely to the indoors. Both cats and dogs can also experience varying degrees of time outdoors, from limited outdoor access (fenced-in yards/parks or on a leash), to free-roaming (free-ranging outdoors, which includes strays and barn cats), and fully feral (little human reliance). 
There are many simple ways to minimize the impacts pets have on the environment—from picking up their poop to keeping them on a leash.

Pets with outdoor access can be involved in hybridization with wild canids and felids, predation on wild animals, and competition for prey with other predators. Even for exclusively indoor animals, disease transmission to wild animals can occur via feces, and pets fed food that includes protein puts pressure on wild fish stocks. 

Seeking harmony

The aim of our paper is not to discourage pet ownership, but simply for pet owners to appreciate the impact their companions can have on the environment. Pet owners can choose to engage in several strategies that will reduce the environmental consequences associated with domesticated animals. The most obvious strategy is to keep cats and dogs strictly indoors or at least be contained indoors over night for the safety of both pets and wildlife. Complete restriction to the indoors is unlikely to ever happen for dogs, and so keeping control of the dog on a leash, allowing off-leash time only in designated areas, and being mindful of wildlife will all reduce the direct impact of dogs. If pets are allowed outside, bells or sonar devices on their collar can reduce predation rates on birds and mammals. Finally, ensuring timely vaccination and removal of outdoor pet feces will reduce the chance of disease transmission to wild animals. Proper adherence to these recommendations would provide owners with the social benefits of having a pet while minimizing the social costs and environmental issues.

The article entitled "Fido, Fluffy, and wildlife conservation: The environmental consequences of domesticated animals" is available on the NRC Research Press website.

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