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A free-ranging dog is any dog that is not contained. The term encompasses various loose categories relating to the ownership, behavior, and descent of such dogs, including wild dogs, feral dogs, stray dogs, street dogs, and village dogs, as well as dogs allowed to come and go freely by their owners. It sometimes overlaps with the polysemic term pariah dog. The term is used when distinctions of ownership are irrelevant.
Rural versus urban free-ranging dogs
Ecologists find it important at times to distinguish between urban free-ranging dogs and rural free-ranging dogs. The distinction can be important as the ecological impact of, and evolutionary pressures on, these groups can be quite different.
Rural free-ranging dogs that rarely if ever leave a settlement are called village dogs. They are considered neither wild nor feral, and have less impact on the surrounding ecosystem than other rural free-ranging dogs. They pose a different set of environmental pressures than feral or wild dogs, or even free-ranging farm dogs. Experts on the behavior of early and primitive dogs have also noted interesting physical and behavioral differences between village dogs and other more feral free-ranging dogs. For example, village dogs tend to be smaller and occur more often alone or in pairs.
Village dogs include the African village dog and East Asian village dog, two types that were the earliest to be domesticated.
The term pariah dog has been used inconsistently, but is sometimes used synonymously, if incorrectly, with 'free-ranging dog'. Originally, it referred to the landrace of free-ranging dogs native to India and other Asian countries. It later came to be used for primitive natural breeds of dogs of a similar physical appearance in other parts of the world. The United Kennel Club has a category of dogs called the Sighthound & Pariah Group, which includes primitive dogs, distinctive local free-ranging landraces, breeds recently developed from naturally selected populations, and very ancient breeds.
Pariah dogs are canids that have kept close to the original form and have evolved with little or no purposeful human intervention. Pariahs in all countries have a very similar, typical morphology known as the "long-term pariah morphotype". This primal body design resembles the ancient breeds from which most other dog forms derive. Typically, these canids have a spitz-like appearance: a wedge-shaped head with a pointed muzzle, almond eyes, erect ears, and a long, tail curved over the back. Unlike modern breeds, pariah dogs have one annual estrus cycle.
Primitive or pariah dogs include the Aspin dog, a native Philippine breed, the Indian Pariah Dog, the Indian Santal dog, the Indonesian Bali Dog, the Korean Jindo Dog, the South African Hottentot dog, and the American Carolina Dog.
Stray versus feral
Experts in the area of free-ranging dog control sometimes distinguish between stray dogs and feral dogs. The former refers to lost and abandoned pets, or others that had socialized to humans before taking to the free-ranging life—and the latter to dogs that have lived all their lives apart from people. This distinction is important to them, because stray dogs can be relatively easily taken into captivity, whereas feral dogs are more fearful and difficult to keep as pets, and so are more often captured, spayed or neutered, and released back into the parks, vacant lots, and other hiding places on the margins of human society where they are most commonly found.
In other contexts, and generally in Indian English, the term "stray dog" covers both feral dogs and dogs that have strayed from their owners. India has a population of feral dogs numbering in the tens of millions, the highest in the world, and millions of people are bitten every year, with about 20,000 people dying annually from rabies. When discussing these issues in the Indian context, distinctions between stray and feral dogs are less clear or important, so the term "stray dog" is used to cover both stray and feral dogs, and to distinguish them from the wild dog of India.
Wild dog may refer to:
- Wild and feral domestic dogs
- Any of several wild canine species that are commonly called 'dogs' or 'wild dogs' but are not true dogs
- Any wild canid—a member of the dog family of carnivores (Canidae), including wolves, jackals, coyotes, foxes, and many more—that are commonly contrasted with 'dogs' in other contexts.
Feral versus wild
In scientific literature, free-ranging dogs such as Australian dingoes are considered 'wild animals' rather than 'feral' to the extent to which they are not 'commensal': dependent on handouts and cast-offs from humans; and instead hunt and scavenge in the wild. Ecologically, wild dogs are integrated into the ecosystem, often as top predators. Evolutionarily, wild dogs are more profoundly changed by many generations apart from people. Both wild dogs and adult feral dogs are less easily kept as pets than free-ranging or captive dogs that have been socialized to humans. Unlike feral dogs, however, wild dogs tend to maintain their wild nature even when taken in as puppies.
True wild dogs
As a technical term, 'wild dogs' is not used in scientific literature to refer to domestic dogs sub-classified as Canis lupus familiaris, no matter how feral or wild they may be. It is reserved exclusively for dogs classified as Canis lupus dingo, which have become more wild animals rather than simply feral: New Guinea singing dogs; Australian dingoes; some Australian dingo/dog hybrids; and others from Southeast Asia and Australasia. While still listed taxonomically as 'domestic dogs', they are considered wild rather than feral domesticated animals, even when raised in captivity. 
Other species called 'wild dog'
Two Canid species have common names specifically calling them 'wild dogs', but are entirely different species from 'domestic dogs' (Canis lupus familiaris): Lycaon pictus, the African wild dog, and Cuon alpinus, the dhole, also called the 'Indian wild dog'. They are not closely related to each other or to true dogs, but may be commonly called simply 'wild dogs' locally or when the species or geographical location is already known or implied.
Other wild canids called 'dogs'
South America has wild canid species that are commonly called 'dogs' in English. These are Atelocynus microtis, "the small-eared dog"; and Speothos venaticus, 'the bush dog'. They are not very closely related to each other and are even more distantly related to true dogs than African and Indian wild dogs.
Not as easily mistaken for a true dog is the wild raccoon dog, Nyctereutes procyonoides, a quite primitive wild canine native to the Far East named for the fact that it looks as if it were a cross between a dog and a raccoon. It is more distantly related to true dogs than any other canid.
Impact on the environment
Feral and stray dogs can have an important impact on environment:
- Predation on wild species 
In 2011, in an article on the Stray Dog Population, the US National Animal Interest Alliance said that the rabies epidemic in stray dogs around the world has transformed into a global public health issue. They also pointed out the following statistics released by the World Health Organization:
- There are 200 million stray dogs worldwide
- More than 55,000 people die from rabies each year
- 15 million receive post exposure vaccines to prevent the disease
- Dogs are the primary source of human rabies deaths
- Vanak, A.B.I. Tamim; Gompper Department Of Fisheries, Matthew E.; Wildlife Sciences, University of Missouri (2009), "Dogs Canis familiaris as carnivores: their role and function in intraguild competition", Mammal Review 39 (4): 265–283, doi:10.1111/j.1365-2907.2009.00148.x, retrieved 2011-08-12
- http://snr.missouri.edu/fw/faculty/pdf/gompper/intraguild-competition.pdf%7C http://snr.missouri.edu/fw/faculty/pdf/gompper/intraguild-competition.pdf
- Dogs: A New Understanding of Canine Origin, Behavior and Evolution - Raymond Coppinger, Lorna Coppinger - Google Books
- Masson, Jeffrey Moussaieff - How Dogs Have Captured Our Hearts for Thousands of Years, ISBN 9780061771095
- Primitive Dogs (Introduction)
- Pet Care | Best Friends Animal Society
- Gardiner Harris (August 6, 2012). "Where Streets Are Thronged With Strays Baring Fangs". The New York Times. Retrieved August 7, 2012.
- U.S. Facing Feral-Dog Crisis
- Review of articles on Dog hybridisation in the wild
- Review of articles on Dog predation on wild species
- Review of articles on Dog predation competition with wild predators
- Review of articles on Dog competition with scavengers
- Review of articles on Dog diseases transmition to wildlife
- Review of articles on rabies transmition
- Review of articles on Canine distemper transmition
- Review of articles on Canine parvovirosis transmition
- "The Global Stray Dog Population Crisis". National Animal Interest Alliance. Retrieved 4 July 2014.
- "Rabies - Fact Sheet N°99, Updated 2013". World Health Organization. Retrieved 4 July 2014.