The Effect of Dogs On Wildlife

Many people enjoy hiking with their dogs in natural areas, since dogs derive a lot of pleasure from sampling all the scents in such areas, as well as getting some great exercise. Some dog owners delight in seeing their dogs roam free off the leash, since the dogs get even more fun from that.

However, due to the disturbance to wildlife caused by dogs, many parks and preserves have banned them. This page lists some of the reasons behind that ban:

Direct Predation. Even though my experience is that dogs are rarely successful in catching the many birds and squirrels they chase, dogs occasionally directly kill wildlife, or injure the wildlife enough to cause their subsequent death.

Packs of dogs are much more efficient hunters, and have been known to kill livestock. This is such a problem that many states have laws authorizing farmers and ranchers to kill any dogs found on their property annoying their livestock.

Dogs roaming off trail can trample vegetation, and if dogs are numerous they can remove the vegetation in popular areas by trampling, scratching and digging. Trampling is the major effect of hikers and their pets to plants.

Indirect Predation. Even when dogs are unsuccessful in catching the object of their chase, the potential prey has had to expend significant energy in order to save their life. Since in many cases animals are just barely surviving, expenditure of extra energy may push them over the edge to malnutrition and allow other predators to kill them. In particular, pregnant wildlife and newborn animals do not have the reserves to repeatedly expend in avoiding dogs. (Effects of Recreation on Rocky Mountain Wildlife: Summary of the September 1999 Review for Montana)

If even 10% of the visitors to the Santa Rosa Plateau brought their dogs on the trail, that would mean over 5,000 dogs chasing or harassing the wildlife during a few months of the year, with most of those dogs concentrated on only a few miles of trail. The effect on wildlife would be substantial.

Both types of predation are severely reduced, but not eliminated, if dogs remain leashed. However the simple fact is that a large percentage of dog owners allow their dogs to be off-leash even when the rules state otherwise. For example, the Angeles National Forest rules require dogs to be on-leash, but at least 90% of the dogs I encounter there are off-leash. Encountering a leashed dog is so unusual that I almost always comment on it.

Disease Transmission. It is worth recalling that the primary effect on Native Americans due to European immigration to the Americas was the importation of disease which killed off the majority of the Native Population. Dogs can apparently transmit a number of pathogens to wildlife:

Many of these pathogens are transmitted through the abundant feces that dogs leave on any trail.

Source: Domestic Dogs in Wildlife Habitats: Effects of Recreation on Rocky Mountain Wildlife.

Competition for Resources. Water is usually the scarcest resource in many places during the summer and fall, especially at the Santa Rosa Plateau. For example, in early October 2001, there are just four small ponds left on the entire Plateau, which are vital to the lives of many of the wildlife species here. Dogs love water, both to cool themselves and to drink, and would therefore be significant consumers of this valuable resource. It would not take many dogs pool visits to deplete these pools of water, thereby killing many individuals that depend on them.

Addition of nitrogen to the soil. Patrick Murphy, a plant ecologist, points out that dog poop adds significant nitrogen to the soil, which encourages the growth of non-native plants at the expense of native plants. (SDUT 12/9/01, E2)

Scent? It has often been said that just the scent left by a dog can affect the behavior of other species. While this certain is plausible, due to the strong importance of scent marking used by animals, apparently this has never been documented. (This does not mean that this is not a problem; simply that it has not been shown to true of false.) See A Review of Mammalian Scent Marking.

Allowing dogs on the trails results in hazards to dogs and their owners as well. The biggest threat is due to the extensive stands of poison oak in the Reserve. Dogs are well-known vectors of the poison oak oil that results in the human members of the dog's family getting poison oak.

There are also large number of plant seeds at the Reserve which are harmful or annoying to dogs. Foxtails and other such grass seeds are in enormous abundance in the grasslands of the Reserve, and can result in serious injury or death to dogs. I have personally paid vet bills of over one thousand dollars due to foxtails causing abscesses and infections in my dogs and cats. Cockleburs cause such huge knots of fur that they usually have to be cut out of the dogs fur. Small hitchhikers such as filaree seeds, bur clover, etc. cause much annoyance as well, requiring significant grooming of dogs after traveling in such areas.

Finally, allowing dogs in the Reserve would significantly decrease the quality of the experience for many visitors:

In case dog owners reading this feel that the above information is simply the opinion of someone who does not like dogs, it is worth noting that I personally have hiked many miles with my dog in public areas where dogs are allowed. Also, both the Reserve Ranger at the Santa Rosa Plateau and the Director of the Santa Margarita Ecological Reserve own dogs that are never allowed on the Reserves themselves due to the prohibitions at both places and the concerns above. So these two people and myself have followed the same restrictions against dogs on Reserves that these Reserves place on everyone.

People and our pets have taken over the vast majority of Southern California. The Santa Rosa Plateau is only 8300 acres where pets are not allowed, compared to millions and millions of acres where pets are allowed. Such small refuges are the only place where animals can live relatively undisturbed by pets.

Other references:

Go to Field Guide to the Santa Rosa Plateau

Copyright © 2001-2005 by Tom Chester.
Permission is freely granted to reproduce any or all of this page as long as credit is given to me at this source:
Comments and feedback: Tom Chester
Updated 22 October 2001 (typo corrected 28 April 2005).