Man's best friend; but an enemy to biodiversity

I’ve been a reluctant dog owner for a long time. I like dogs - don’t get me wrong. I just happen to me allergic to dogs. On the other hand, I am not allergic to my wife and children; and they love having dogs. So that’s that.

I do though understand why dogs are the most beloved animal companions on the planet - loyal, affectionate, and deeply woven into our daily lives.

There are over a billion pet dogs worldwide, making them not just common pets but also, as Philip Bateman and Lauren Gilson point out in a new article, the most abundant large carnivore on Earth.

But the emotional bond we share with dogs may be blinding us to an uncomfortable truth: their presence - more specifically, our behaviour as dog owners - is having devastating environmental consequences.

I looked into the environmental impact of pets when I wrote The Earth Transformed.

So, for example, in the UK, people in the UK spend around £4bn a year on pet food. That figure is dwarfed by what American pet owners spend: in 2022, they forked out an estimated $58bn on food for their pets.

Globally, pet food requires about twice the size of the UK to grow food; pet food produces more than 100m tons of carbon emissions each year.

As it happens, I didn’t include any of the research that I’d read - because you can’t cover everything. But I have kept an eye on this field ever since.

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A lot of work has been done on cats (feral and domestic): for example, a recent paper suggested that cats kill over 1 million birds, 1.67 million reptiles and nearly 3 million mammals in Australia. Every single day.

Dogs don’t get so much attention - maybe because of better marketing as ‘man’s best friend’; maybe because they don’t seem to do so much damage. Eiher way, the role of pet dogs in degrading biodiversity, spreading zoonoses, and polluting ecosystems is poorly understood and - according to this latest work - vastly underappreciated.

Even well-fed and well-behaved dogs retain instinctive predatory traits. They chase, harass, and sometimes kill wildlife: for example, in Tasmania alone, owned dogs were responsible for 91% of all reported penguin deaths at monitored colonies between 1980 and 2020. One dog wearing a collar (and thus likely owned) killed up to 500 Brown Kiwis in just five weeks.

But the threat goes far beyond direct attacks. Studies cited in the article show that dogs, whether on the leash or not - cause measurable stress responses in animals, leading to habitat abandonment and energy depletion. For long-distance migratory birds, even brief disturbances can push their energy budgets beyond breaking point, threatening survival and reproduction. Dogs don’t look like trouble-makers; but they often are.

Perhaps even more insidious are the indirect impacts of dogs, for dogs don’t need to be seen to be feared. Scents left by dogs - through urine, faeces, and glandular secretions - can deter wildlife from foraging or nesting in otherwise safe areas. Over time, this alters population dynamics and reshapes ecosystems.

The mess that gets left behind is a real nuisance (even in leafy Oxford).

Dog waste isn’t just unsightly; it’s ecologically disruptive. A single dog produces over 1000 kg of faeces and 2000 litres of urine in its lifetime. That’s a lot.

In cities and parks where dog densities are high, the cumulative nitrogen loading in waterways and soils rivals that of industrial pollution. In some urban areas, dog urine is the largest single contributor of nitrogen runoff into local ecosystems.

Add to this the chemical runoff from anti-parasite treatments, like fipronil and permethrin, which enter streams when dogs swim or are bathed. These insecticides can be lethal to aquatic invertebrates and leave traces that last for weeks. Even dog hair brushed out and used by birds as nesting material has been linked to increased chick mortality due to pesticide contamination.

And then we should also consider the environmental footprint of feeding our pets.

That’s something I looked at for Earth Transformed: the global dog food industry accounts for 56–151 million tonnes of CO₂ emissions annually, equivalent to the output of a mid-sized industrialised nation.

Food for dogs uses up as much as 1.2% of all global agricultural land - about twice the size of the UK in other words. It also diverts up to 13.5% of the global forage fish catch away from human consumption to pet food production.

And yet, most dog owners (however environmentally conscious in other aspects of life) are usually unaware of this pawprint. Even when aware, few are willing to switch to sustainable dog food alternatives, especially as prices for such products rise. According to one recent survey, fewer than 16% of owners were willing to pay more for greener food options.

Bateman and Lauren Gilson are clear about what the real problems are: first, there are a LOT of dogs. Second, most owners are either unaware of the damage their pets cause or unwilling to take meaningful responsibility.

In many places, simple behavioural changes could make a difference. Keeping dogs leashed in sensitive areas, respecting seasonal bans and getting everyone to pick up waste could dramatically reduce the harm caused. But as the authors note, compliance is often low. In Australia, just one in five and in some cases one in ten owners observed leash laws even in vulnerable bird nesting zones. Social media is filled with images of unleashed dogs chasing wildlife while signs are ignored and volunteers are harassed.

This, the authors argue, is a classic tragedy of the commons: many dog owners entitled to roam public spaces, assuming that their actions alone don’t matter. But the cumulative result is environmental degradation at large scale. Without a strong sense of collective responsibility, plus a regulatory enforcement to back it up, many vulnerable ecosystems will continue to suffer.

Despite my own problems with dogs, none of this is to say that we need to give up our beloved pets dogs. As other research shows, companionship is psychologically and socially invaluable. Dogs can even be allies in conservation - as scent-detection dogs trained to locate rare or invasive species have demonstrated.

But this potential is squandered if we don’t also acknowledge the negative impact of pet ownership and take action to limit it.

If we truly care about animals, that compassion must extend to the wildlife and habitats threatened by our choices. The challenge ahead is not simply one of managing dogs, but of managing ourselves.

More soon.