Generally speaking, stray dogs are ones that live on the streets without having an owner, or that have lived their lives without being domesticated. Stray dogs usually feed on any rubbish that is left outside, which is why you find them close to populated areas. Some of the animals, although living wildly on the streets, are fed by people. This is why in the English language they are known as "community dogs".
The presence of stray dogs leads to many problems. From an animal welfare point of view, the biggest problems are the unpredictable and bad conditions for living. The dogs are lacking basic things like water and food, as well as protection from the heat and the cold. Often the overpopulation is countered by killing the animals or by catching them and putting them into animal shelters which is detrimental and causes a further deterioration of the quality of life. The euthanasia of these animals hardly ever follows veterinary standards. Unethical methods like poisoning the animals are widely spread. A second aspect is the transmission of zoonoses. Zoonoses are referred to as diseases that can be transmitted from an animal to a person or vice versa. A common example is rabies. Stray dogs can be carriers for such diseases and thus their presence poses a risk of infection for humans. Often the mere fear of such diseases leads to individual dogs or whole populations being killed.
In Germany stray dogs don't exist. Of course one has to remember that the Germans are generally very fond of their animals, and dogs that live in the house with the family are commonplace. In many countries,however, dogs are considered more "livestock" than pets. The benefits of their presence vary from guard and defense functions to herding flocks, even to draft purposes (in the polar regions). In many countries, dogs lead lives that are not associated with a domestic lifestyle and, therefore, reproduce uncontrollably. The source of stray dog populations are always owned dogs, which produce unwanted offspring which "flows" into the population of strays. To understand the dynamics of a stray dog population, one has to know some basic things.
This refers to the fact that a fixed area of a species only provides resources for a certain number of individuals, to exist in this environment without significant harm to the habitat. In Layman's terms: If a room is full, nobody else will fit in it. Referring to stray dogs, limiting factors are based on access to the following resources:
Thus, the number of stray dogs stays approximately the same in a fixed area, as nature uses the existing resources. If you remove animals of this population (for example by imprisoning them in a shelter or by euthanasia, which is, unfortunately, still practiced in many countries around the world), the population deficit is immediately offset by a higher birth rate, immigration of animals from outside and higher life expectancy of the remaining animals. The remaining animals have access to more food and more water. The main factor for the refill are births of puppies within the population, and to a limited extent the abandonment, by people, of puppies or adult animals so the animals are forced into this stray population.
Many hundreds of thousands of dogs worldwide have already been poisoned, clubbed to death, euthanized or killed in other ways to solve the stray dog problem. But all these barbaric methods only lead to a short term decrease in the population density. The only recognized and functioning approach to influence a population long term, is the castration of animals in the population and at the same time leaving these animals in their area. This ensures that no other dog can occupy this place during the lifetime of the animal. If the entire population is castrated and one also prevents the other growth options (abandoning of dogs, immigration from outside), the problem could be solved within one generation of dogs. Especially in remote areas and on islands one can see an enormous effect of neutering campaigns after a short time.
The main problem is that too few organizations are specialized in castrations and often their commitment to conduct such campaigns lasts only for a short time. Our experience has taught us that both long-term project loyalty and massive presence are two of the most important factors to ensure a long-term reduction in the population of stray animals.