How pet dogs harm wildlife and the environment

An estimated 1 billion domesticated dogs live around the world. Most have owners and share their lives with people as pets, companions or working animals.

Dogs are the world's most numerous large predator. Pet cats are a distant second, numbering around 220 million.

The harm that owned and feral cats can cause wildlife is widely recognised. Feral dogs are also often regarded as a threat to biodiversity, although dingoes can play a positive role.

Our pet dogs, on the other hand, often appear to escape scrutiny.

Unfortunately, that exemption rests more on sentiment than evidence. The impact our much-loved dogs have on wildlife and the environment is greater, more insidious and more troubling than we might wish to believe.

Our new research sets out the damage pet dogs cause and the measures that can address it.

Dogs are predators that catch many kinds of wildlife, sometimes injuring or killing them. Their scent and droppings frighten smaller animals. Feeding these carnivores also carries a substantial environmental cost, as does the sheer amount of poo they produce.

We love our pet dogs, but that love comes with a real cost. We need to acknowledge it and protect wildlife by keeping our animals on leads or otherwise restrained.

The pet dog as a predator in your home

Dogs are domesticated wolves, selectively bred to be smaller, more docile and highly responsive to people. Even so, they remain predators.

Wildlife care centre data show that more attacks on wildlife are reported for pet dogs than for cats, and that dogs catch larger animals.

In Tasmania, pet dogs off the lead are the principal reason little penguin colonies are close to collapse.

One escaped pet dog in New Zealand is estimated to have killed as many as 500 brown kiwis from a population of 900 in just five weeks.

When dogs are let off the lead, they enjoy chasing birds and other animals. It can look harmless.

However, a chase can drain already tired migratory birds, making them expend more energy. Dogs can also kill the fledglings of birds that nest on beaches, including endangered species such as the hooded plover.

For many birds and other animals, the presence of these predators alone is frightening. Wildlife remains on high alert even when dogs are on leads. Across woodland sites in eastern Australia, this has measurable adverse effects on the abundance and diversity of birds.

In the United States, deer become more alert and flee sooner and farther when they see a person with a dog on a lead than when they see a person alone.

Several US mammal species regarded a dog accompanied by a person as a greater threat than coyotes.

Dogs need not be present to affect wildlife. They mark trees and posts with urine and leave faeces in many places, signalling danger to numerous other species. US researchers found that animals including deer, foxes and even bobcats avoided places where dogs were regularly walked, compared with dog exclusion zones, because of the traces dogs left behind.

The cost of keeping dogs healthy and fed

Flea and tick treatments given to pet dogs can remain on their fur for weeks and wash off when they enter a creek or river. Some contain ingredients that are highly toxic to aquatic invertebrates, so even a brief swim can be devastating.

Researchers have also found that when birds such as blue tits and great tits gather brushed-out dog fur to line their nests, fewer eggs can hatch and more hatchlings can die.

Then there is the poo. The US has around 90 million pet dogs, compared with 12 million in the UK and 6 million in Australia.

An average dog produces 200 grams of faeces and 400 millilitres of urine each day. Over a 13-year lifespan, that amounts to a metric tonne of faeces and 2,000 litres of urine. Across the dog population, the result is a mountain of waste.

This waste can contribute to nitrogen pollution in waterways, change soil chemistry and even transmit diseases to humans and other wildlife. Over 80 per cent of pathogens that infect domesticated animals also infect wildlife.

Because dogs eat largely meat, millions of cows and chickens are raised solely to feed our pets. Feeding dogs worldwide produces roughly the same emissions as the Philippines and has a land-use "pawprint" twice the size of the UK.

No one likes thinking about this

People love their dogs, who are always pleased to see us. Their companionship benefits both our physical and mental health, and many farms could not operate without working dogs. We would rather not admit that dogs can cause harm too.

Of course, dogs are not bad. They are animals with natural instincts, alongside the domesticated instinct to please us. Yet their vast numbers mean they cause real damage.

Many of us have a sizeable dog-shaped blind spot. We think little Brutus would never do anything like that. But Brutus can and does.

The decision to own a dog brings responsibilities. A good owner cares not only for their beloved animal, but also for the wider natural world.

Bill Bateman, Associate Professor, Behavioural Ecology, Curtin University, and Lauren Gilson, Research Associate, Behavioural Ecology, Curtin University

This article is republished from The Conversation under a Creative Commons licence. Read the original article.