The environmental and health impacts of allowing cats outdoors

Ashley Hoffman- Natural Resource Conservation

Blake Lucas- Animal Science

Heather Moulding- Animal Science




Richard Conniff walked out his door one day only to notice an array of desiccated corpses, belonging to birds and small mammals, scattered about his walkway. Could all of these be “offerings” from his beloved cat, Lucky?  Unknowingly, Conniff was allowing his outdoor cat to be the perpetrator of up to 33 birds and dozens of mammal deaths yearly.  His desire to let a predator such as Lucky live a free-spirited lifestyle, had consequences beyond his realization. (Conniff, 2014)

Almost as if Karma had planned it, Lucky fell victim to the same fate that she had forced upon many others before.  One night, she and another neighborhood cat were attacked and killed by a wild animal. Conniff found the bloody remains of his companion the next morning and was devastated. Coincidently, a bobcat had jetted out in front of his car when leaving his neighborhood that same morning.  Surely, he thought, this must be the ruthless killer of the crimes the night before. (Conniff, 2014)


The Problem


Allowing your cat free roam of outside poses many problems for both your pet and your community. Like Conniff’s cat Lucky, other outdoor cats can easily be killed from other predators or become the victims of a wide variety of tragic accidents.  The domestic cat is not native to most ecosystems, so their “natural” environment is not the outdoors (Duffy & Capece, 2012).  Outdoor cats are the direct cause of the overpopulation of the feral cat community, contribute to the spread of  diseases and reduce small animal populations (Duffy & Capece, 2012).  When owners allow their cats outdoors, they put everyone at risk, including their cat. Methods of enrichment should be considered in replace of  unlimited outside access to stop this problem.


Why let your cat outdoors?

The desire to let a cat outdoors often stems from owners wanting their pet to live a more “natural” life.  In a study, conducted by Salo and Stone (2014), veterinary opinions were collected to assess the views on indoor versus outdoor cat living.  They found that most participating veterinarians understood that cat owners provide outdoor access because they want their cats to enjoy the outdoors (Salo & Stone, 2014).  Cat owners regard their cat crying or escaping through the door as a moderate reason for permitting their pets outside access (Salo & Stone, 2014,).  In addition, a significant number of participants believed that cat owners want to reduce furniture damage and do not want to clean or smell a dirty litter box (Salo & Stone, 2014).  Largely, veterinarians believe that rodent control is only a minor contributing factor in a cat owner’s decision (Salo & Stone, 2014).  

Knowing this, veterinarians should be doing more to combat the issue.  Cat owners need to be made aware of the risks and alternatives available to them in regard to cat enrichment. Allowing cats outdoors poses serious health and environmental concerns that can be prevented by pet owner education, especially from veterinarians.



Motor Vehicle Accidents


An outdoor cat lives an average of one to five years, while an indoor cat lives an average from eight to twelve years (Mathews, 2015). The great outdoors posses several tragic possibilities for cats. Cats do not have the innate instinct to avoid busy streets and this can lead to to fatal accidents. Cats can travel large distances in one day and that can additionally increase the probability of a cat getting run over. There are as many as 190 million motor vehicles on the road in the United States and an estimated one million animals are killed or injured daily. That equates to one animal every 11.5 seconds (Braunstein, 2015). This study includes many types of animals, but cats clearly still have a great chance of a fatal accident.  Cats are also a hazard to people because drivers will often swerve or hesitate when they see a cat in the road. Such incidents can lead to car wrecks, sometimes involving other cars.


Diseases and Illness


Veterinarians suggest that “because stray cats often carry dangerous diseases, the best thing that you can do to protect your domesticated cat against serious illness is to keep it indoors” (Pendle, 2015). When your cat is inside it has little to no chance of fighting with other animals, which could lead to the spreading of diseases through wounds. Feline leukemia, FIV (HIV) virus and feline panleukopenia are just a few of the illnesses a cat is capable of contracting. Rabies is also a common virus among many different animals. If bitten, a cat becomes very unpredictable and can transfer the deadly virus to anyone it comes in contact with. Although rabies is curable in the beginning, many cats are euthanized due  to this disease. Additionally, outdoor cats can contract intestinal worms, fleas, ticks and ear mites from that could be brought into the home. These parasites can transfer and multiply, potentially causing a Lyme disease outbreak in the cat’s household. Furthermore, keeping a cat indoors can prevents kidney failure that can come as a result of ingesting poisonous substances, such as antifreeze (Pendle, 2015). Keeping your cat indoors can lessen it’s exposure to all these potential illnesses and keep you pet happy and healthy.


Predation by Other Animals


Cats are subject to predation by many different types of animals if allowed outdoors. Cats are considered a favorite by foxes, coyotes, hawks, and even raccoons. A farmer complained about losing sixteen cats within a couple of months. He found scattered cat remains in his barn but no signs of who the culprit was. A professional was called to the farm to find one overweight raccoon later that night (Cabrera, 2009). The raccoon would feast on the animal, eating a little each night. This was only one of many examples of domestic cats ending up as prey. The safety of a house can ensured the protection of beloved cats if the owners are educated about the problem. However, even with the predation of cats, the United States still has an overwhelming feral cat population due to owners allowing cats outdoor access.


Overpopulation of Cats


A cat’s chance of pregnancy greatly increases if allowed outside unattended. A fertile cat can reproduce two times a year, generating four to eight kittens a litter (Conniff, 2014). An owner can go from having one cat to nine cats within a matter of months. This problem adds to the already overpopulated feral cat population. An estimated 50 million feral cats live in the United States alone and they significantly contribute to overcrowded animal shelters (Williams, 2013). Additionally, feral cats further the spread of many diseases putting your cat at greater risk.


Environmental Impacts of Outdoor Living


It is important to realize that domesticated cats are not a native part of most ecosystems  and have the same devastating effect on the environment as so many other non-native species do. Cats are considered an invasive species. They are opportunistic predators who will hunt and kill even when they are not hungry. No populations of native species are safe (Duffy & Capece, 2012).

In areas with high populations of outdoor cats, there is a significant decrease in bird, small mammal, and reptile populations (van Heezik et al., 2010). A study, conducted in New Zealand, monitored one hundred and forty four outdoor house cats, in a particular area, to determine what type  of prey the cats were taking and how many of each species (van Heezik et al., 2010). In this survey, it was discovered that birds were killed the most by the monitored cats (van Heezik et al., 2010). According to the authors, “83% of cats that brought back prey caught birds” (van Heezik et al., 2010, p. 2). Outdoor cats also preyed on small mammals and reptiles, which lead to a decline in the populations of certain species (van Heezik et al., 2010). The authors state that, of the cats that brought back prey, 39% killed mice, 39% killed rats and 17% captures skinks (a type of lizard) (van Heezik et al., 2010, p. 2). Keep in mind that each individual cat can kill multiple types of prey, so these statistics will not add up to 100%. The predation of native species due to outdoor cats was calculated through cat predation models from the data retrieved from this survey. The estimated results for all species was that extinction is highly likely over a significant period of constant outdoor cat predation (van Heezik et al., 2010).

In addition, outdoor cats are arguably the largest anthropogenic cause of bird and mammal deaths in the United States. They have lead to the extinction of numerous wildlife species across the globe (Loss et al,, 2013). The Union for the Conservation of Nature (IUCN) has documented that 14% of modern bird, mammal and reptile extinctions on islands are partly by outdoor cats (Loss et al, 2013, p.2).  Such extinctions include the deer mouse on Estanque Island, Mexico and the last population of Stephen Island wren in New Zealand (Duffy & Capece, 2012). Although it is difficult to determine the exact mortality rate of species caused by outdoor cats, it is determined that they kill approximately 1.3-4.0 billion birds and 6.3-22.3 billion mammals yearly (Loss et al., 2013, p. 1).  If that wasn’t enough, it is claimed that between 228 and 871 million reptiles and between 86 and 320 million amphibians are killed by cats annually within the United States (Loss et al., 2013, p.4). Invasive species are causing mass extinctions of native populations all around the world and the domestic cat is a contributing factor to this.

The reduction and extinction of native populations due to the predation of outdoor cats can have a devastating effect on the surrounding environment. Outdoor cats create additional interspecific competition in the food webs of the ecosystems they inhabit (Chase et al., 2002). Cats are skilled, predators that are usually taken care of by humans. This gives them an advantage over other native predators, such as foxes and birds of prey (Chase et al., 2002).  When cats reduce the prey species for these predators, the predators are forced to either compete intraspecifically, or within the species, leave the ecosystem in search of prey, or starve to death.  It is also possible that they could switch prey  species, which puts your cat on the menu (Chase et al., 2002). Cat predation could also cause an increase in the organisms that birds and small mammals consume, especially insects and other small invertebrates (Chase et al., 2002). This imbalance in the food chain has the potential to cause the whole ecosystem to collapse.  It may also allow additional non-native species to move in and take over this reduced and extinct species niches (Chase et al., 2002). Outdoor cats have the potential to alter the entire native ecosystem just by doing what comes naturally to them.

Implementing Education


There are many solutions and alternatives to letting your cat roam outside. It is our belief that the solution starts with communication and education.  Veterinarians are a pet owners’ trusted counselor for guidance, but when it comes to swaying an owner on what to do with their pet from a “non-medical” standpoint, many feel uncomfortable providing an opinion (Salo & Stone, 2014).  Salo and Stone (2014) found that 49% of participants believed that veterinarians are where a cat owner is most likely to gain advice from in relation to behavioral issues (p. 2).  Additionally, 91% of those veterinarians agreed that there are increased risks in allowing your cat outdoors and these dangers should be conveyed to all clientele (Salo & Stone, 2014, p. 1).  Unfortunately, only 66% of these participants actually suggested to pet owners to keep their cat indoors (Salo & Stone, 2014, p. 1).  What leads to this discrepancy?

The majority of veterinarians agree that outdoor cats are a concern and owners need to be  more aware of their cat’s actions, but not all are comfortable speaking up.  Some veterinarians feel that this discussion is not their area of expertise, so we propose that this topic be integrated into the veterinary curriculum.  Seventy one percent of veterinarians agree that cat housing is important to discuss and should be a part of veterinary education (Salo & Stone, 2014, p. 2).

In order to reach cat owners who do not use veterinarians or do not consider their advice, we would like to additionally inform people through advertisement on cat foods. A simple fact or chart displaying the negative health or environmental impacts a cat can have by being allowed outside could help in our quest of educating cat owners. Knowledge is said to be power, and if cat owners become informed, they can to make the right decisions for their pets.


Owning a Pet is a Responsibility


The habit of simply opening the door for your cat to go outside will be difficult for most owners to break. The outdoors provides entertainment, exercise, and a place to go to the bathroom without the burden of a stinky litter box.  It is also believed to be a more natural way of living, which owners often feel is important for their cat’s happiness (Salo & Stone, 2014).

You want your cat to live a long and happy life, but giving them free roam of the neighborhood is not the solution.  By providing care and meeting your cat’s daily exercise requirement, they will be just as content resting by your side indoors then they would hunting down prey outdoors.  Letting them outside may be easiest, but it is far from the safest which should be of the utmost importance.  Being a responsible pet owner goes beyond convenience.

Instead of free range of the outdoors, cats should be given alternative enrichment which allows for the safety of the cat and the environment.  There are many options available that cat owners are not aware of.  Below, we have mentioned a fair amount of these alternatives that should relate to people of all backgrounds and financial situations.


Pet Owner Concerns and Solutions


Cat owners should consider leash walking or constructing a “catio” (outdoor enclosure) for their cats to enjoy the fresh air (Enriching your cat’s life, 2015). These suggestions will keep your cat safe and provide most of the benefits of being outside. Daily play times with your kitty is also very important to provide a sufficient amount of enrichment and exercise (Enriching your cat’s life, 2015).  If your cat will not walk on a leash or constructing a catio is infeasible, then as suggested in Enriching your cat’s Life, written by the ASPCA (2015), buying a variety of toys that satisfy your cat’s curiosity has the potential to provide a sufficient amount of exercise and stimulation.  Often times, the cheaper or simpler toys can be some of the most interesting for a cat.  Something as simple as a string attached to a stick is a very feasible option for all cat owners.   However, owners need to be involved and active with their cat for these methods to succeed. If you are someone who cannot move around easily during play with your cat, you may want to consider buying a laser pointer.  This gives you the ability to sit down while still playing a game of chase with your cat using the laser.  These can be found in pet aisles at a surprisingly low cost.

In regards to the litter box, people committing to a cat should expect that there is maintenance to their ownership.  Cats are misrepresented as the “maintenance-free” pet, but this is not so.  Potential cat adopters need to be aware of the work that comes with responsibly owning a cat.  This includes cleaning a litter box and keeping your cat inside or in an enclosed, safe area.

Litter boxes can be cheap, but buying litter every week or cleaning it out is a tedious task for a lot of people.  Saving up for an automatic litter pan could be beneficial for your lifestyle if you want to own a cat but do not want the dirtiness of a typical box.  You can buy these types of litter boxes at your local Petco or other pet supply stores.  There are even some litter pans that easily attach to the plumbing of your toilet and self-clean without the need for scooping or buying litter each week.

Another concern some cat owners may have is simply not having enough room in their small apartment or residence.  In this circumstance, we suggest building up for your cat instead of cluttering your limited floor space with cat objects.  By building cat shelves on your walls, you can effectively utilize the space in your home while pleasing your cat (Galaxy, 2015).  Since many cats are natural tree dwellers who love being up high, any amount of space off the floor that you can provide for them is excellent (Galaxy, 2015). Cats also love climbing in and on cabinets, refrigerators, and desks. If the owner doesn’t mind, the cat will easily make use of all the space he or she lives in.


Concluding Thoughts


Some owners claim that being outside allows cats to lead a more “natural” lifestyle. However cats were the first domesticated animals and scientist say they actually domesticated themselves. Living closer to humans made it easier for cats to find food and shelter and soon became dependent on humans for survival (David Brown, 2007). Animal domestication is the decrease in wild behavior and the increase of human interaction for survival. Statistically speaking, house cats have longer, healthier lives than their wild, or feral, counterparts. We believe that this makes them happier too.

Additionally, we are aware that, even with our efforts, not everyone will keep their cats indoors. However, if we can reduce the number of cats preying on native species, even just slightly, it will help to stabilize a link in the food web for native species. We would like to conclude our thoughts by stating that through education and our proposals we can ensure the utmost safety and enjoyment for each owner and his or her cat. By keeping cats indoors we can prevent these dangerous health and environmental impacts within our community.




Braunstein, M. (2015). Driving animals to their graves. Culture Change. Retrieved April 5, 2015 from


Brown, D. (2007, June 29). Why do cats hang around us. The Washington Post. Retrieved April 5,2015 from


Cabrera, K. (2009, January 19).  Raccoon predation on domestic cats. Animal Tracks. Retrieved April 4, 2015 from


Chase, J. M. , Abrams, P. A. , Grover, J. P. , Diehl, S. , Chesson, P. , Holt, R. D. , Richards, S.A., Nisbet, R. M. and Case, T. J. (2002), The interaction between predation and competition: a review and synthesis. Ecology Letters, 5: 302–315. doi: 10.1046/j.1461-0248.2002.00315.x


Conniff, R. (2014, March 21). The evil of the outdoor cat. The New York Times. Retrieved April 6, 2015, from


Duffy, D. C., & Capece, P. (2012). Biology and impacts of Pacific island invasive species. 7. The domestic cat (Felis catus). Pacific Science, 66(2), 173-212. doi:10.2984/66.2.7


Enriching your cat’s life. (2015). ASPCA. Retrieved April 28, 2015, from


Galaxy, J. (2015). Climbing & perching. Retrieved April 28, 2015, from


Loss, S.R., Will, T., & Marra, P.P. (2013). The impact of free-ranging domestic cats on wildlife of the United States. Nature Communications, 4(1396), 1-8. doi: 10.1038/ncomms2380


Pendle, C. (2015). 5 Most dangerous cat diseases. Animal Planet. Retrieved April 5, 2015 from


Salo, A., & Stone, E. (2014). A survey of the views of US veterinary teaching faculty to owned cat housing practices. Journal of Feline Medicine and Surgery, 1-4. doi: 10.1177/1098612X14561503


Williams, G. (2012, November 6). US is over run with more than 50 million cats. Aljazeera American. Retrieved April 4, 2015 from


Winsa, P. (1996). Road kill. GTA. Retrieved April 5, 2015 from


van Heezik, Y., Smyth, A., Adams, A., & Gordon, J. (2010). Do domestic cats impose an     unsustainable harvest on urban bird populations? Biological Conservation, 143(1),            121-130. doi:10.1016/j.biocon.2009.09.013



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