Bad dog? The environmental effects of owned dogs

Introduction

Dogs are the most popular pets in the world. There are approximately 90 million pet dogs in the USA, 12 million in the UK (Dog Population by Country 2024), and about 6 million in Australia (Animal Medicines Australia 2022). Dog ownership is estimated at over a billion animals worldwide, making domestic dogs the most common vertebrate predator worldwide (Gompper 2014). This total comprises mostly dogs that are ‘pets’, i.e. companion (or working) animals that have an owner and are under a human’s control most of the time, and does not encompass free-roaming domestic/semi-feral dogs that must forage for their own food (numbers of such unrestrained dogs are difficult to estimate because they cannot be reliably obtained through pet-ownership surveys). Here, we use the term ‘owned dogs’ (sensuRitchie et al. 2014) in our discussion of problems associated with human-mediated dog presence and impacts.

While both owned and feral cats are repeatedly (and rightly) implicated in the destruction of wildlife and the reduction of biodiversity globally (Doherty et al. 2017; Trouwborst et al. 2020; Woolley et al. 2020), owned dogs are rarely perceived as problematic to biodiversity, despite the acknowledgement of feral dogs as threatening both to wildlife survival (e.g. Silva-Rodríguez et al. 2010) and to the integrity of biodiversity through interbreeding with wild canids (Leonard et al. 2013; Randi et al. 2014; Mallil et al. 2020). However, data from wildlife care centres indicate that owned dogs are responsible for more recorded attacks on wildlife than cats (Holderness-Roddam and McQuillan 2014). Owned dogs (62%) have been recorded as catching a higher proportion of native animal prey in Australia than owned cats (47%), and also take larger prey (Franklin et al. 2021). We argue that the impact of owned dogs on the environment is far greater, more insidious, and more concerning than is generally recognised.

The impacts of owned dogs can be direct, indirect, highly localised and wide ranging. In this review, we address the scope of these impacts ranging from predatory behaviour to direct disturbance, to mere presence disturbing wild animals, to the natural and unnatural residues of dogs in the environment, and finally to the huge environmental impact of owned dogs through the pet food industry.

A cascade of effects of owned dogs on the environment

Dogs are predators – the only large carnivore that has been domesticated. Even as pets, they retain their predatory behaviour despite artificial selection that has resulted in many ‘breeds’ of dog becoming physically very different from their wolf (Canis lupus) ancestors from which they diverged at least 16,000 YBP somewhere in Eurasia (Perri et al. 2021).

The cascade of direct impacts of owned dogs

The most obvious predatory behaviour retained by dogs is that of chasing other species. The predatory behaviour of dogs has been previously discussed by Ritchie et al. (2014), who point out that ‘pet’ or ‘owned’ dogs may have limited or restricted potential to interact with wildlife but nonetheless still do so when they accompany humans into natural areas. Direct predatory behaviour can occur even close to home; indeed, a study of admissions to a wildlife rehabilitation facility in Queensland, Australia indicated that dog attacks accounted for 9.2% of admissions (primarily mammals and reptiles), and that mortality was highest (72.7%) among these dog-associated admissions (Taylor-Brown et al. 2019).

The negative effects of dogs on wildlife in natural areas are often inextricably linked to the behaviour of their owners. A particularly egregious example is that of unrestrained owned dogs attacking Little Penguins (Eudyptula minor) at colonies in Tasmania, where modelling has indicated that regardless of colony size, dog attacks can be severe enough to lead to colony collapse (Blamey et al. 2024). Between 1980 and 2020, 55 mortality events at colonies were due to dog attacks, which represents 91% (887 deaths) of all penguins reported dead. Blamey et al. (2024) point out that penguins of multiple species are susceptible to dog attacks; e.g. African Penguins (Spheniscus demersus) in South Africa (Vanstreels et al. 2019), and Galápagos Penguins (Spheniscus mendiculus) on the Galápagos Islands (Barnett 1986). While some of these attacks are from feral dogs, owned dogs are frequently implicated. A presumably escaped, owned dog (with a collar) killed 13 of 23 Brown Kiwis (Apteryx australis) with trackers – an extrapolation to kiwis in the population without trackers resulted in an estimate of up to 500 kiwis killed over a 5-week period from a population of 900 kiwis (Taborsky 1988). Off-leash owned dogs have been observed using adaptive hunting techniques to get close to potential prey – a dog on a beach lunging from the cover of breaking waves to attempt to catch Silver Gulls (Chroicocephalus novaehollandiae) on a beach in Western Australia and another using a dry stream bed in the Darwin Botanic Gardens in the Northern Territory to stalk an Orange-footed Scrubfowl (Megapodius reinwardt) (Fulton 2014).

It is important to recognise that an animal does not have to be caught and/or killed by a dog to suffer. Shore-nesting birds are particularly susceptible to disturbance by owned dogs. In Western Australia, off-leash dogs were believed to be responsible for killing chicks of the endangered Fairy Tern (Sternula nereis nereis), but also with numerous disturbances of breeding birds by running through beach colonies (Greenwell and Dunlop 2023). Breeding Kentish Plover (Charadrius alexandrinus) in Spain were flushed from their breeding beaches between 50 and 100% of the time when lone dogs were present; plovers were flushed 93.8% of the time if a human was with the dog but responded to humans alone only 12.9–47.6% of the time (Gómez-Serrano 2021). Similarly, unleashed dogs were reported as a disproportionate source of disturbance for Snowy Plovers (Anarhynchus nivosus) at a site in California, USA (Lafferty 2001). This disturbance is not cost-free for the birds; it was estimated that 10 alarm flights per day elicited by leashed and unleashed dogs (also walkers with no dogs) could increase daily energy expenditure by 4.5–4.7% for Knots (Calidris canutus and Calidris tenuirostris) and 7.5–7.8% for Sand Plovers (Charadrius mongolus and Charadrius leschenaultii) in northern Australia (Lilleyman et al. 2016). This is of particular concern for long-distance migrants whose energy reserves have already been depleted by their annual migratory flights where disturbance alone, without pursuit or contact, could prove fatal. While such indirect mortality is challenging to quantify, it is nonetheless a real concern for biodiversity conservation on beaches that are significant stopovers for migrant bird species. It is also a significant responsibility for owners of dogs using those beaches to control the behaviour of their pets.

Neither dogs, nor most people, can be expected to discriminate between migrant and local bird ‘stimuli’, and therefore the potential severity of the disturbance, but neither should this influence the owners’ behaviour, who have a responsibility to be aware and to manage both themselves and their animals. Dog harassment of wildlife can be an actionable legal offence, and regulations exist, and yet poor compliance by owners is common (Schneider et al. 2020).

These data on the impact of dogs’ natural predatory behaviour suggest that a simple way to mitigate the worst effects of disturbance by dogs is to keep them leashed on beaches and maintain a buffer distance from nesting or roosting shorebirds. Unfortunately, many dog owners disagree. Dowling and Weston (1999) showed that rules posted to prevent disturbance to the nesting vulnerable Hooded Plovers (Thinornis rubricollis) at a site in Victoria, Australia, were broadly ignored by visitors; leash laws were particularly flouted, with only 12–22% of dogs being leashed. Similarly low compliance with leash laws (<25%) was recorded at a breeding site for Piping Plovers (Charadrius melodus) in Nebraska, USA, despite the dog walkers themselves expressing both concern for the plover and support for the leash laws (Jorgensen and Brown 2014). At Fort Funston in California, USA, attempts were made to prevent dogs accessing habitat near colonies of Cliff Swallows (Riparia riparia), where dogs were also observed digging in vegetation restoration areas and damaging rare plants; the local dog walkers’ association denied the negative effect of the dogs (McCall 2007).

Social media are good sources for highlighting the ubiquity and extent of unleashed dog disturbance; e.g. eight unleashed dogs recorded within 1 h at a Hooded Plover nesting site in Victoria, Australia (Dooley, S [@Twitchathon] [2023, December 31]. X [Twitter] https://x.com/Twitchathon/status/1741264231885111768 ‘Hats off to the incredible @BirdlifeOz beach-nesting birds volunteers who have to put up with all types of ignorant, entitled, aggressive beachgoers when trying to keep nesting Hooded Plovers safe’); an unleashed dog chasing seabirds from a mudflat in the UK (Denton, I [@IanDenton12] [2024, November 23]. X [Twitter] https://x.com/IanDenton12/status/1860291968565215442 ‘The Casual Harassment of Nature.’) (Fig. 1). Seasonal dog restrictions on beaches with breeding birds exist (e.g. Maguire et al. 2019) but this relies heavily on owner participation and resources to allow enforcement of these rules. Dog owners on beaches in Victoria, Australia show low compliance with posted rules, although it is highest for ‘No Dog’ areas (Maguire et al. 2019), and enforcement of such rules by authorities such as patrols, is expensive (Dowling and Weston 1999).

Fig. 1.

Social media recording of negative effects of dogs. Dogs off-leash, on-leash, present in an area even on trails, non-collection of dog faeces, and collective amounts of faeces all have significant effects on wildlife and the environment.

The insidious nature of the negative effect of dogs is indicated by the influence of even leashed animals: many of the reports on dog disturbance cited by Weston and Stankowich (2014) refer to leashed dogs that are under control. Such dogs are still perceived by many wildlife species as threatening predators – the human-mediated spread of dogs means that they have been a presence in most ecosystems for thousands of years and are established as a recognisable predator globally (Doherty et al. 2017). A comparison of effects of humans with leashed dogs, humans without dogs, and a control of no humans or dogs in New South Wales, Australia, showed that dog-walking had the greatest negative effect on bird abundance and diversity across multiple woodland sites (Banks and Bryant 2007). Mule deer (Odocoileus hemionus) in California, USA, were on average alert sooner, flushed sooner, and fled farther when approached by a human with a dog off-trail (100.6 m, 81.94 m, >300 m, respectively) than by a human alone (66.7 m, 34.19 m, 77 m, respectively) (Miller et al. 2001). In the south-eastern USA, a community-science camera trap study in protected areas showed that white-tailed deer (Odocoileus virginianus), eastern grey squirrel (Sciurus carolinensis) and raccoon (Procyon lotor) all temporally, but not spatially, avoided dogs and humans, which were perceived as higher risk than were humans alone, or coyotes (Canis latrans) (Parsons et al. 2016). However, a Canadian study found no effect on diversity of birds or small mammals of dog presence in parks, whether dogs were on- or off-leash (Forrest and St. Clair 2006).

The cascade of indirect impacts of owned dogs

Dogs that enter fresh water, even if not in pursuit of wildlife, can have a significant negative effect on this environment. Topical flea/tick medications applied to a dog’s fur wash off into natural waterways and cause non-target mortality, affecting aquatic invertebrate taxa (Teerlink et al. 2017; Perkins et al. 2021; Diepens et al. 2023; Perkins and Goulson 2023). Up to 86% of fipronil, an anti-flea and tick insecticide applied to dogs, rinses off when the dog is washed, or enters water, and is toxic to aquatic invertebrates at low concentrations (Teerlink et al. 2017). Again, social media provides good examples of this issue, e.g. (Lees, A. [@Alexander_Lees] (2024, July 2024). X [Twitter] https://x.com/Alexander_Lees/status/1814628030335095257‘Ubiquitous example of the tension with free public access to important wildlife sites at @DerbysWildlife Lightwood: public disregard for signage with dogs spreading invasive aquatic plants and likely killing aquatic fauna with pet flea treatments’, posted with images of signage requesting people ‘keep dogs on leads and out of water’ at a nature reserve, and a video of an off-leash dog entering a stream at the site.

Topical flea/tick drugs medications containing Fipronil, imadicloprid, and permethrin can last several weeks; brushed out hair and fur is often used as a nest liner by birds and can be highly toxic: a recent study showed that nests of Blue Tits (Cyanistes caeruleus) and Great Tits (Parus major) lined with fur with more insecticide types or higher concentration of insecticides were more likely have dead offspring or unhatched eggs (Tassin de Montaigu et al. 2025).

Even when dogs are not present in an area, they can still have an effect. Dogs leave glandular scent marks, faeces, urine, and other traces that effectively indicate ‘presence of predators’ to multiple wildlife taxa even in their physical absence. A comparison of natural areas in the western US where dogs were either allowed or prohibited on trails showed that both mule deer and small mammals were less active within 50–100 m of trails where dogs were walked compared to areas with no dogs; and both red fox (Vulpes vulpes) and bobcat (Felis rufus) were detected less frequently in areas that allowed dogs (Lenth et al. 2008). However, Ramírez-Cruz (2020) demonstrated that the ringtail (Bassariscus astutus) in urban southern Mexico did not avoid areas where more dogs were walked (indicated by presence of dog faeces), which may have been due to a level of habituation and temporal partitioning.

It has been calculated that ‘an average dog produces around 0.2 kg faeces and 0.4 L urine per day’; over a life of 13 years, this totals over 1000 kg of faeces and 2000 L of urine per dog (Yavor et al. 2020). Urine impacts soil chemistry in urban areas with many dogs; dog urine can potentially become the greatest contributor to nitrogen in urban waterways (Allen et al. 2020). Dogs and their faeces can also be vectors and reservoirs for broad range of zoonoses that affect wildlife and humans (Mendoza Roldan and Otranto 2023). Dog faeces collected from tourist sites in Sardinia tested positive for the intestinal nematode Strongyloides stercoralis, Toxocara sp. roundworms, and the whipworm Trichuris vulpis (Tamponi et al. 2020). In the Gran Paradiso National Park in Italy, domestic working dogs threaten wildlife with canine distemper virus, Toxoplasma gondii, and the protozoan parasite Neospora caninum (Costanzi et al. 2021). Over 80% of pathogens that infect domesticated animals also infect wildlife: for example, canine distemper from domestic dogs can spread to lions (Panthera leo) and spotted hyaenas (Crocuta crocuta) amongst other species in the Masai Mara-Serengeti ecosystem (Alexander et al. 1995; Cleaveland et al. 2000). Rabies from domesticated dogs has been implicated in the decline of endangered Ethiopian wolves (Canis simensis) (Randall et al. 2004) and African wild dogs (Lycaon pictus) (Gascoyne et al. 1993). Most of these threats are intensified by the sheer number of dogs globally, together with the behaviour of dog owners: in Australia legislated dog waste management in public spaces requires owners to collect their dogs’ faeces in plastic bags to dispose of in landfill bins (Bryson et al. 2024); however, this does not always happen (see Fig. 1). Some imaginative attempts have been made to encourage compliance; for example, in Mexico City, a scheme was introduced where deposition of dog faeces in a container that also housed a router rewarding the dog owner with a set number of free Wi-Fi minutes (https://edition.cnn.com/2012/05/07/tech/swapping-dog-poop-for-free-wi-fi/index.html).

Finally, the environmental ‘paw print’ of the dog food industry is recognised as enormous and growing (Martens et al. 2019): pet food production environmental impacts – greenhouse gas emissions (56–151 Mt CO₂), agricultural land use (0.8–1.2% of global agricultural land use), and freshwater use (0.2–0.4% of water extraction for agriculture) – are calculated as equivalent to the footprint of almost twice the UK land area and has the greenhouse gas emissions equivalent to the 60th highest emitting country (Alexander et al. 2020). It has been estimated that up to 13.5% of the 39 million tonnes annual catch of wild forage fish (small schooling fish typically prey of other fish) is not eaten by humans but goes to pet food production (De Silva and Turchini 2008).

So what?

It is all well and good to point out the environmental issues involved with owned dogs (Fig. 2), the problem lies in identifying solutions. Pet companionship is hugely important to people (e.g. Hardie et al. 2023), and dogs, both as companions and working animals, will continue to have vital roles, including in conservation through their use as detection dogs (e.g. Grimm-Seyfarth et al. 2021). The issues we have highlighted here spring from two main variables: (1) the sheer number of dogs globally; and (2) the lax or uninformed behaviour of dog owners. The first of these seems almost insuperably difficult to surmount. While it is recognised that the dog food industry should be included in any nation’s sustainability action due to its considerable environmental footprint (Martens et al. 2019; Alexander et al. 2020), dog owners express reluctance to shift to more sustainable dog foods (Conway and Saker 2018) that are more costly to produce. Only 12–16% of surveyed dog owners said they would be willing to pay more for sustainable dog food; perhaps understandable as median prices for sustainable pet food increased by 22% in 2023 (Phillips-Donaldson 2024).

Fig. 2.

Negative effects of dogs on the environment include (a) predatory behaviour and chasing, resulting in fleeing by wildlife, with effects on mortality, energetics and reproduction, (b) presence in an area, resulting in effects on diversity and abundance of multiple taxa, with possible effects on reproduction, (c) entering water, with wash-off veterinary products affecting diversity and abundance of invertebrate taxa, possible subsequent effects on aquatic vertebrates, and (d) presence of urine and faeces, with increases in nitrogen in water courses, effects on health of vegetation, and spread of zoonoses and parasites. (Prepared with BioRender).

It might be expected that dog owner behaviour would be easier to remedy; however, as intimated above, there is much ignorance (perhaps understandable) among dog owners regarding the effects of dogs on the environment, together with recalcitrance towards taking responsibility for and mitigating their dogs’ impacts. An extreme example is reported by Fulton (2022), who was threatened with violence when asking people not to drive cars or walk dogs on a protected beach that prohibited these activities. These patterns persist despite the generally favourable opinions towards the environment expressed by dog owners (e.g. Jorgensen and Brown 2014). Much of this conflict may result from a ‘tragedy of the commons’ analogy when it relates to a communal resource such as a beach or woodland where dogs and their owners may enjoy exercise. It may be understandable that an individual owner sees no reason to not use such a resource when others do so, and hence contributes to the accumulative environmental degradation of the site. In the absence of community feeling of shared responsibility for public spaces, all that is left is restrictive or prohibitive actions – banning of dogs from multiple vulnerable sites. Indeed, this is the only choice for sites with vulnerable breeding birds, particularly beaches (see Fig. 1), though with limited resources typical of most conservation groups, policing of any breaches of dog-access regulations is often difficult (Maguire 2018).

The problem with owned dogs and their environment will not just go away. There needs to be a dialogue on how we can maintain our important relationship with companion animals and balance that with a meaningful, sustainable stewardship of the environments on which both people and their dogs and resident or migratory wildlife depend.