In many developing nations, dogs roaming freely around human habitations are common. These dogs lead scavenger lifestyles that depend on human waste for survival. Understanding the population dynamics of free-ranging dogs is necessary for their effective management. Birth weight and infant mortality are significant determinants of mammal life histories. To understand the pattern of population growth and the factors affecting early life mortality in free-ranging dogs, we conducted a five-year census-based study in seven West Bengal, India, locations. Only 19% of the 364 pups from the 95 observed litters made it to adulthood, and 63% of total mortality was caused by humans, which is a high rate of mortality. The relationship between dogs and people on the streets is extremely complex because while living close to people increases the availability of resources for dogs, it also has significant negative effects on their population growth.
Gray wolves (Canis lupus lupus), the ancestors of free-ranging dogs (Canis lupus familiaris), were domesticated and have since spread throughout human settlements1,2,3,4,5,6. They have been able to coexist with humans in both urban and rural habitats as scavengers7,8. Their primary sources of food are domestic animal carcasses, openly disposed human leftovers, and food obtained from humans through begging9,10. Free-ranging dogs interact frequently with people and rely heavily on them for food, but they are frequently viewed as a threat because they can spread disease and pathogens11,12,13. On occasion, dogs will attack people in the street, especially at night when a car passes through a dog’s territory. These dogs roam freely and are frequently viewed as a serious threat to human health because they are rabies, canine distemper, and parvovirus reservoirs11,12,13. For instance, 99% of all rabies-related fatalities in humans take place in underdeveloped nations, with dog bites accounting for the majority of cases10 Growth in the number of stray dogs is facilitated by exponential human population growth13. When humans do not fully control the movement and reproduction of free-ranging dogs, it poses a significant problem for health management in developing nations. Vaccination and contraception programs for animals are costly and only likely to be successful if implemented widely14,15. Improved food waste management may also aid in lowering the number of stray dogs near populated areas16. However, in developing nations, such management becomes even more challenging, and management choices must be based on an understanding of the ecology and population dynamics of free-ranging dogs, for which there is a dearth of scientific data17,18.
Free-ranging dogs in India are facultatively social, and social interactions during mating and dening seasons have a significant impact on group dynamics19. Despite having two distinct mating seasons, they have only been reported to breed once a year20 (Sen Majumder and Bhadra, 2015). Mothers and other group members exhibit a significant amount of cooperative behavior toward newborn pups, which is anticipated to increase the pups’ survival rates21. Around 8 weeks old, puppies begin to wean themselves, which also signals the beginning of resource disputes with their mothers22,23. Dogs go through pup (birth to three months), juvenile (three to six months), and sexual maturation stages (six to nine months) before reaching sexual maturity. The social structure is quite dynamic in the adult (after reaching sexual maturity) and sub-adult (after six months to reaching sexual maturity) stages24 due to the prevalence of dispersals. Although research on the behavior and cognitive capabilities of dogs is expanding26,27,28,29, in-depth studies of the structure and dynamics of naturally occurring free-ranging dog populations are still lacking. Mammal life histories have been compared, and it has been found that mortality in juveniles is more strongly correlated with life history traits than mortality in adults, and that in females, the age of onset of reproduction is strongly correlated with life expectancy at birth30,31. We hypothesize that high early life mortality may be a significant factor influencing population growth in free-ranging dogs since many births are observed in these animals each year but growth does not appear to be very high13,32. In this study, we estimate the early-life mortality rates of dogs that roam freely and analyze the factors that affect their survival. Puppies were monitored from birth until the end of the seventh month of their life or until they died, whichever came first, as the onset of sexual maturity in dogs begins at 6 months of age. This makes sure that when estimating early life mortality, we took into account the entire juvenile period and excluded individuals who were sexually mature.
Pups began to appear in the population in October, and between the months of December and January, the number of pups and juveniles peaked. The average litter size at birth was 3. There was no bias toward any particular sex (Male: Female: 1:1) and the results were 98 2 (median 4, quartiles 3-5, N = 108) 4. The Mann Whitney U test result was U = 5621, df = 104, 104, and P = 0. 625). Beginning in January, the death/disappearance rate surpassed the birth rate, and the population’s net number of pups and juveniles started to decline significantly (Linear regression: R2 = 0). 848, β = −0. 921, P = 0. 003, Supplementary Information 1), with no more pups being born after the month of February () Only 18. 96% of all puppies that were seen at 7 months old were still alive. Dog age and survival had a negative correlation (Linear Regression: R2 = 0 985, β = −0. 992, P < 0. 0001,) and this trend persisted over the sampling period of five years (comparison using linear regression: F = 1). 412, P = 0. 254). The highest rate of mortality (30. 47%) was observed at the 4th month of age.
A plot of the pups’ survival probabilities according to each ordered time at which the event of removal occurred was produced by the survival analysis () The median of the curve is 82 days (95%CL: 72-92 days; N = 364). The variables “sex” and “habitat” showed a significant effect on survival time in the Cox mixed-effect model (Supplementary Information 2). shows the stratified survival curves for males and females separately. The median value of survival time for females was 112. 5 days (N = 164, 95% CL: 93-136 days), whereas it was much lower for men, at 80 days. 5 days (N = 156, 95% CL: 68–92 days). A log-rank test confirmed a significant difference (Chisq = 8. 1, df = 1, p = 0. 0045) between the two curves, demonstrating that males had significantly lower survival probabilities than females. separately displays the stratified survival curves for the urban and suburban populations. In comparison to the suburban population, which had a median survival time of 71 days (N = 214, 95%CL: 59-86 days), the urban population’s median survival time was 95 days (N = 150, 95%CL: 75-149 days). Log-rank test confirmed a significant difference (Chisq = 26. 7, df = 1, p = 2. 33e–07) between the two curves. Nevertheless, male and female survival rates remained similar across the two habitat types (as sex and habitat alone had no impact on mortality) (Supplementary Information 2, Model 6).
Only 32% of all deaths were due to natural causes, and 5% of all deaths lacked reliable records. Human activity affected the remaining 63% of total mortality either directly (accidents, poisoning, or beatings) or indirectly (taking from the population). At the age group 0-1 month, natural causes accounted for 52% of deaths, whereas only 3% of deaths were caused by human activity. The prevalence of human-influenced death or disappearance peaked at 1 month of age (50%) and persisted through the 5th month. Juveniles going missing from the fifth month onwards accounted for 70–80% of all deaths, indicating the beginning of population dispersal.
The cumulative incidence curve () displayed the percentage of people who were removed from the population over time for a particular reason in the presence of other competing reasons. For categories 2 (taken by humans) and 4 (road accidents), men and women showed statistically significant differences in incidences (;) This implied that female pups experienced more traffic accidents and that humans took male pups away preferentially. The incidences of categories 1 (natural death) and 3 (murder by human) differed significantly between urban and suburban habitats (Supplementary Information 3), indicating greater human intervention in suburban habitats.
With an expected male:female ratio of 1:3, the simulation model (Supplementary Information 4) produced a population that was highly skewed at 7 months. 53, compared to a much better sex ratio of 1:1 in the general population. 56. However, the model and the data showed a similar trend for the distribution of sexes at each age group, indicating that the observed skew was the result of pure chance. Therefore, the higher rate of female road fatalities was caused by the selective eradication of male pups from the population rather than a genetic tendency for females to be more accident-prone.
Only about 19% of puppies in free-ranging dogs were sexually mature when they were young, which indicates a very high early mortality rate and an even lower lifetime survival rate. In the population of free-ranging dogs, the pattern of mortality over pup age in months did not change over the course of the four years of sampling, and is therefore considered to be the true trend. According to an earlier report, 67% of pups died by their fourth month of life33, the highest rate of mortality was seen during this time. This can be attributed to juveniles’ increased mobility and the beginning of dispersal around the fourth month of life25,34. Additionally, our data revealed a rise in the number of missing people after the fifth month of life, which may indicate increased dispersal. Studies on other canids that inhabit areas near human settlements have also suggested that juveniles experience higher mortality rates than adults35,36,37.
Free-ranging dogs are not an exception to the fact that humans have been linked to a significant number of species’ deaths, including coyotes and foxes that coexist with people in both rural and urban settings38,39,40,41,42. The majority of these studies point to hunting and/or road kills as human-caused causes of animal deaths in human-dominated landscapes. Additionally, our study found that 62 percent of deaths or disappearances were caused by human-influenced factors. Interesting, after the first month of age, when pups are no longer in the protective environment of dens and social play increases, the human-influenced deaths increased and remained high43,44. As a result, around this time, humans are more likely to cause accidents to puppies and to take advantage of them by taking them away for adoption or other reasons. This leads to an increase in human-influenced mortality, including cruelty to the puppies.
Intriguingly, urban areas have higher overall mortality rates than semi-urban areas due to both natural and human factors. In the suburbs, where human densities are lower than in cities, the pups and juveniles were not only more likely to die of natural causes like disease and starvation, but they were also more likely to experience human interference in their lives. This difference in mortality rates is likely due to the relatively lower dog-human interaction in cities and the greater availability of resources and shelters there16. These findings are consistent with observations of carnivores like red foxes (Vulpes vulpes), coyotes (Canis latrans), Eurasian badgers (Meles meles), and raccoons (Procyon lotor) that have not only adapted to urban habitats but have also taken advantage of human-made shelters and food sources to achieve higher population densities than in natural habitats42. Therefore, in order to manage free-ranging dog populations in urban habitats more effectively, it is important to comprehend the dependence of dogs on humans for their survival16 and the anthropogenic factors, such as socio-cultural factors15, that may have an impact on their population dynamics later in life.
Due to the extreme skew in the numbers of male and female pups/juveniles in the resulting population, our simulation demonstrates that people preferentially remove male pups from the population, which results in higher mortality of females from accidents. Therefore, humans not only contribute significantly to the early-life mortality of dogs living in the wild, but they also skew the sex ratio of the cohort that reaches sexual maturity. When both adults and juveniles are taken into account, a random sample from West Bengal’s population of free-ranging dogs has shown that the sex ratio in the dog population does not significantly deviate from 1:132. The fact that we noticed a skew in the sex ratio at 7 months of age suggests that elements like adult mortality and dispersion can cause the sex ratio to stabilize. Indeed, based on our simulation, it appears that the skew itself may increase female mortality later in life as a result of both natural and artificially caused factors. Further research after our observations may be important for providing important leads for effective and humane management of free-ranging dog populations in India and other nations that face comparable problems with free-ranging dogs because infant mortality and juvenile mortality are significant factors that shape life-history traits in mammals30,31.
Between 2010 and 2015, free-ranging dogs were sampled using a census method (scan sampling while walking along a predetermined route), in a variety of locations throughout West Bengal, India, including urban and semi-urban habitats. The following West Bengal, India, regions were examined in the study: Saltlake (22 5800° N, 88. 4200° E), Kalyani (22. 9750° N, 88. 4344° E), IISER-K campus in Mohanpur (22. 9638° N, 88. 5246° E), Batanagar (22. 29° N, 88. 11° E), Garia (22. 4598948° N, 88. 3894769° E), Howrah (22. 59° N, 88. 31° E) and Ramnagar, East Midnapore (21. 47° N, 87. 45° E). The localities, which included both residential and commercial areas, were chosen at random based on how easy it would be to sample within areas where people live. Each of those areas had a study area that was 1-2 km2. The observer walked on all roads and lanes in the pre-selected area at least twice and, ideally, three times a day to look for pups. According to the size of the study area, each visit took 1-2 hours. When puppies were seen, a note was made that included information about the location of the litter, the size of the litter, the gender of the puppies, and their approximate date of birth when the precise date of birth was unknown. These details were used later to track individual pups. 95 of these litters, totaling 364 pups, were monitored until they were 7 months old. We recorded the causes of death for each pup death (or disappearance) case, either through direct observations or by relying on reports from the locals. We carried out linear regression analyses in StatixtiXL version 1. 11 to compare the data from various years and to comprehend the pattern of mortality in the population.
Between 2010 and 2015, 108 mother-litter groups of free-ranging dogs were found. Of these, 95 litters, totaling 364 pups, were tracked up until the seventh month of age, while the remaining 13 litters, totaling 66 pups, had information available only at birth. Tracking was based on the body patch locations and coat color. All deceases and disappearances were categorized as mortality. The various factors that led to death could be roughly divided into human-influenced deaths (poisoning, beating, malnutrition, road accidents, taken away from the population), natural causes (disease, climatic factors, predation by other dogs or jackals, and injury from fights), and disappearances for unknown reasons. Humans (mostly children) frequently take puppies away, and our qualitative observations reveal that while some of these puppies are adopted as pets, the majority are abandoned. Unless they are further adopted by other people, the abandoned puppies usually perish from starvation. If abandoned puppies are not returned to their own packs, they frequently encounter adult dogs’ aggression and have a low chance of survival. Since humans effectively removed pups and juveniles from the gene pool, they were treated as dead for the purposes of this analysis unless we observed that they returned to their natal groups during the course of our observations.
The probability that a person survives past a certain time t is what determines the survival function S(t) in the survival analysis. In our case, “survival” refers to remaining alive within the population, so all individuals who were eliminated from the population due to various causes were deemed to have “not-survived.” The age in days of the person at the time the “event” of his or her removal occurred is referred to as the “survival time.” Death or removal is also frequently referred to as a “failure” The individuals’ survival times are regarded as “right-censored” because they were monitored until 30 weeks of age and no information about their survival times is available after that point. We used the ‘Survival’ package47,48 of the statistical computation software R49 to conduct a survival analysis45,46 by the Kaplan-Meir (KM) method in order to comprehend the impact of the various factors in determining the population structure of free-ranging dogs. The survival curve is produced by the ‘Survfit’ function of the ‘KM method,’ where the independent variable is survival time and the dependent variable is the survival function S(t). Estimates of KM survival for urban and suburban populations, as well as for males and females separately () We used the Cox proportional hazard (PH) model50 to examine the impact of the explanatory variables litter size, sex, and habitat on the duration of individual survival. With the aid of the “coxme” package51 of R and the raw data (for details, see Supplementary Note 5), the Cox modified chi-square statistic was used to compare differences in the type of death for each sex.
For each age class (0-1 month, 1-2 month, 1-2 month, 2-3 month, and so on until 7 month of pup age), we examined the impact of all types of causes (natural death, human-influenced death, disappearance or gone missing from the population, and death or disappearance due to unknown reasons) behind pups’ mortality. Later, we divided the “human influenced death” category into three subcategories, such as “taken by humans,” “murdered by humans,” and “death in road accidents.”
To comprehend the contributions of different factors to mortality in the population, we used competing risk analysis. We divided the event of “death” into various categories. Given that multiple events are thus possible, the person can only encounter one of the numerous distinct types of events during the study period. These categorical events include “natural death,” “taken by human,” “murdered by human,” “death in traffic accident,” and “no information” (which includes “missing” and “unknown”). Using R’s ‘cmprsk’ package52, we modeled competing risks survival data using a cumulative incidence curve (CIC). In the presence of competing events, CIC estimates the marginal probability of an event. For comparisons, a modified chi-square statistic53 was used to account for variations in incidence between the sexes.
We were curious about the observation that more women than men died in traffic accidents, so we decided to test whether this observation was due to a skew brought on by the selective removal of men, or whether women are inherently more likely to die in traffic accidents. With a starting population of 1000 dogs and a sex ratio of 1:1, we ran a simulation using the observed mortality rates. The model utilized both mortality rates incurred by humans and those incurred by other species.
No dogs were harmed during this work. The work described here was all observation-based, and no dogs were ever handled in any way. The animal ethics committee at IISER Kolkata approved the methods used in this paper (approval number: 1385/ac/10/CPCSEA), and they also complied with the Government of India’s approved regulations on animal rights.
How to cite this article: Paul, M. et al. Humans have a significant impact on free-ranging dogs’ high early life mortality rates. Sci. Rep. 6, 19641; doi: 10. 1038/srep19641 (2016).
We would like to thank Mr. For his assistance with the simulation model for mortality in R, Bishwarup Paul, Department of Biological Science, Indian Institute of Science Education and Research, Kolkata The Council for Scientific and Industrial Research, the Indian National Science Academy, the SERB, the Department of Science and Technology, and IISER Kolkata, all of India, provided funding for this work.
Contributions of the Author M. conducted the field research for this article. P. , S. S. M. and S. S. , A. K. N. and M. P. carried out the survival analysis and P. H. model; M. P. carried out the rest of the analysis. A. B. designed, oversaw the project, and wrote the paper with M. P. and A. K. N.
Can stray dogs survive in the wild?
Due to their historical connections to wild dogs like the small South Asian Wolf, dogs today, both domesticated and feral, are able to survive in the wild quite well. Dogs, who have lived alongside humans for about 10,000 years, were likely the first domesticated animals.
A feral animal is one that is untamed or wild. Consider a feral dog as a wolf or bear-like creature that was born in the wild. Feral dogs have never interacted with people, or if they have, they have come to understand that people are simply a part of their surroundings. They are independent of people and do not require them because, like other wild animals, they have adapted to live in our world and are self-sufficient. Even if humans are their source of food, animals do not associate them with it because they view a porch, yard, a bowl of food left out, or a trash can as just another element of their surroundings.
Although there are fewer feral dogs in the United States, they do exist. Many times, these stray dogs are born in the “wild” and have never interacted with people. Although wild dogs typically do not live as long as their domesticated counterparts do, they also do not always lead unhappy lives. This is because they are accustomed to living like other wild animals and are unaware of what it is like to have a pet dog. Although it may be challenging, a feral dog has the same mentality as a deer, fox, or even a bear. A truly feral dog should be approached with caution.
There are numerous strays who are incapable of taking care of themselves. This is due to the fact that these dogs have occasionally needed to rely on people. Strays have occasionally interacted or received some socialization from people and other dogs. The interactions these dogs had with people before they became stray determine whether or not they trust people. Strays may have spent months or even years being raised by humans before becoming stray for any number of reasons, including natural disasters, human neglect and abandonment, getting lost, or any other scenario. Many people will try to fit in with their surroundings, but in reality, their lives are much shorter than those of a stray dog because they lack the coping mechanisms that strays do.
How difficult is it to rehabilitate stray dogs and feral dogs? is one of the frequent queries I receive. To start, it’s critical to define “feral dogs.” There is a significant difference between the terms “stray” and “feral,” despite the fact that I have heard them used interchangeably.
The majority of wild dogs are very skilled and at ease with being dogs. Although they don’t always fear people, they tend to avoid them because, as I said earlier, people are weak in comparison to them or are not a part of their pack. Feral dogs are frequently found in groups of one or more canines or even as a family. Although feral dogs, like any other wild animal, are not always aggressive, they will defend themselves if threatened. They have a high level of survival intelligence, are very adaptable, and have no other way of life. Wild dogs become accustomed to their environment and profit from opportunities that are presented to them. These dogs are simply a part of the culture and environment and are not dependent on humans.
PETA needs to hold off on advocating for stray dogs on the streets of the US until it does so in India.
According to WHO recommendations, sterilization of pets is not advised, not for homeless dogs who are already struggling to survive. Another reason killing stray dogs doesn’t work is because it, like ABC, concentrates on the problem’s symptoms (homeless dogs on the streets) rather than its root cause (pets).
There is also no ‘Indian context’ to the WHO guidelines. The WHO-recommended sterilization program was and is still only for PETS.
Unowned dogs on the streets have an average life span of three years, struggle to survive and have very low fecundity and litter survival rates. Consider also the problems of pet retention. People are often unable to keep their pets for their entire life span for a number of reasons — moving house, having kids, pet having litters often, other financial, behavioural space or time constraints.
Methods aimed at pets should have the biggest impact because they are the group of animals that reproduce the most successfully. Strategies that solely rely on reducing the number of dogs are ineffective in the long run because the animals are already struggling to survive and are unable to reproduce. Due to their potential importance in the spread of rabies and other diseases, these dogs may need to be the focus of control measures.
FAQ
Do stray dogs survive?
Unless they are further adopted by other people, the abandoned puppies usually perish from starvation. If abandoned puppies are not returned to their own packs, they frequently encounter adult dogs’ aggression and have a low chance of survival.
How long does a Indian street dog live?
Indian mongrels usually have a life span of 5-6 years. Some people do, however, frequently live for longer than 14 years. Animal activists in Noida claim that stray dogs, particularly those of the “Indian Mongrel” breed, are subject to the most abuse and contempt from locals and the general public.
How can you tell how old a street dog is?
The researchers point out that the Indian Native dog, also known as the Indian Pariah dog, typically dwells on the streets and subsists on donations from the public and trash. They reside anywhere from large cities to the edges of forests, either alone or in small groups. They have wolf-like faces, patchy coats, and short fur.