Dogs in the Chernobyl exclusion zone

On April 25, 1986, a safety test was conducted on Chernobyl’s Unit 4 reactor during a planned maintenance shutdown. Operators attempted to determine whether slowing the turbine could provide enough power to cool the reactor in the event of an outage. Miscommunication between the test engineers and plant safety staff led to the reactor operating under unstable conditions. The resulting power surge caused fuel damage, steam buildup, and two explosions early on April 26 - one from steam pressure and another likely from the buildup of hydrogen^[1] . The blasts ignited fires and released radioactive material into the atmosphere, prompting the evacuation of nearby residents within a 30-kilometer zone that later became known as the Chernobyl Exclusion Zone ^[2] .

After the 1986 nuclear disaster in Chernobyl, the regional domestic dog population suffered from environmental pollution originating from the radiation. This disaster made the environment highly mutagenic, leading to various evolutionary processes including, but not limited to, bottlenecks, directional selection, and higher rates of mutation resulting in evolutionary trajectories that differ from unexposed animals.^[3]

The exact origin of the populations of dogs living in the Chernobyl Nuclear Power Plant (CNPP) and the surrounding areas of the Chernobyl Exclusion Zone is unknown.^[3] However, it is hypothesized that these animals are the descendants of pets left behind during the original evacuation of Pripyat. Following the 1986 Chernobyl disaster, residents were ordered to evacuate with less than an hours notice, leaving most of their animals behind^[4] . While many of these original pets population were killed by the Ukrainian Ministry of Internal Affairs to prevent the further spread of radiation,^[5] some dogs are believed to have survived by avoiding culling efforts and were soon after cared for by cleanup workers in the Exclusion Zone.^[3] Those that survived, reproduced. There are currently two geographically and genetically distinct populations of dogs in the area, one in the CNPP and one in Chernobyl City.^[3] Scientists discovered this by implementing tracking and survey programs and conducted genetic analyses of the two dog populations. These studies showed limited gene flow and strong genetic differentiation despite the groups being only about 16 kilometers apart. ^[3]

In 2017, researchers launched the Chernobyl Dog Research Initiative after noticing that the number of stray dogs in the Exclusion Zone had grown dramatically, with estimates suggesting a population of more than 800 animals. Three temporary veterinary centers were tasked with examining and testing geographic diversity within the populations living within and outside of the Chernobyl Nuclear Power Plant (CNPP). In total, blood was drawn from 302 dogs, including 132 living inside of the CNPP, 154 in Chernobyl City and 16 outside of the CNPP. The study found that the feral dogs tend to form packs of related individuals with different family groups often living close together. This pattern likely reflects how feral dogs adjust their behavior and territory in response to human presence and food availability. The complex social structure of these populations suggests that random mating may not apply to the dogs of Chernobyl.^[3]

When tested for genetic differences, the results of dogs living in the Chernobyl Exclusion Zone (CEZ) suggest that these populations have lived in the region since the nuclear disaster or earlier and could serve as a model for studying the long-term effects of radiation exposure. Results how show that dogs from both the CNPP and Chernobyl City share traits most commonly found in free-breeding dog populations rather than purebreds, indicating natural rather than artificially selected breeding. The CNPP dogs are more genetically isolated, possibly due to restricted human access and physical barriers, while Chernobyl City dogs show limited modern breed influence, such as mastiff and flock guardian ancestry, which could have been introduced by returning residents and their accompanying pets. DNA evidence indicates older genetic contributions from shepherd breeds and more recent ones from pinscher breeds, providing a timeline of breed introduction and radiation exposure. Overall, the CNPP population appears to be the most direct descendant of the original post-disaster dogs, making these groups valuable for understanding how prolonged environmental radiation influences animal genomes.^[3]

At least 15 families are living inside the CEZ are mostly related to shepherd breeds such as the German shepherds, characteristics shared by other feral dogs living in Eastern Europe.^[6]

Analysis of the genetic diversity within these populations showed varying levels of heterozygosity between them. Dogs from Chernobyl city showed the highest levels of genetic diversity due to high rates of heterozygosity, indicating an outbred population. To contrast, the lower rates exhibited in dogs from Pripyat suggests increased inbreeding. Populations from the Semikhody train station and ISF2 displayed similar levels while individuals in Slavutych showed lower median levels of heterozygosity despite their wide dispersion. ^[3]

The dogs suffer from radiation that may differentiate them genetically from the population of CEZ with their surroundings. Nevertheless, processes such as the high likelihood of inbreeding can lead to difficulties at the moment of analyzing their genome. In addition, the conditions of their habitat, human control in the access to the CEZ, may simulate an island habitat in terms of evolutionary processes such as isolation.^[3]

Despite the evidence of genetic differentiation mainly due to the radioactive environment, there is no support for pinpoint radiation as the primary driver of genetic differentiation; the evidence serves as insight for further research in these populations. Some regions of the genome indicate that they can be driven by directional selection. 391 outlier loci are influenced by directional selection, with at least 52 candidate genes.^[7]

Genetic signatures of the Chernobyl dog populations have been compared to both pure-bred and free-breeding dog population genetic structures. The Chernobyl populations did not share increased similarity to pure-bred dogs, indicating that the populations of dogs of Chernobyl have not been inundated with individuals that are modern pets. Instead, this population is similar to free-breeding populations, indicating that the population has been established at least since the disaster in 1986. However, the Chernobyl dogs show enough differentiation from these populations that they can be used as a unique entity for further genomic study.^[3]

Dr. Megan Dillon has done substantial research in determining genetic differences between the two populations of Chernobyl dogs, classifying them as Chernobyl City (CC) and Nuclear Power Plant (NPP) through factors such as pathogenic prevalence in ticks and genetic diversity on the chromosomal level. ^{[8] [9]}

Dr. Dillon's work with pathogenic prevalence in ticks showed a significant difference in exposures in these two locations. The results should show that most ticks in the CEZ are Ixodus ricinus (castor bean tick) with a very small population of Dermator reticulatus (ornate cow tick). 56.9% of I. ricinus were contaminated with 1+ pathogens, and with this knowledge, there was a substantially higher amount of bacteria contained in the ticks in the NPP (44% A. phagocytophilum and 42% B. burgdorferi) than CC (23.1% A. phagocytophilum and 19% B. burgdorferi). Despite this, there was a much lower level of A. phagocytophilum in the NPP dogs than in the CC dogs (1.8% and 11.7%). Despite all of this information, tick-borne parasites were equal for both populations.^[9]

Dr Dillon's focus on the genetic diversity between the populations used karyotypic architecture, quantification of genetic differentiation, short tandem repeat (microsatellite) analysis, and count of derived alleles. With these methods at the disposal of researchers, the karyotypic architecture collected eight samples, four from each of the two populations of dogs; however, seven of these samples managed to produce sufficient quality of metaphase spreads for analysis, and no abnormalities were observed.^[8] For quantifying genetic differentiation between the two populations in the CEZ and unaffected dogs in Eastern Europe, the fixation index was significantly different for all values. The CC dogs were less significantly different from Eastern European populations, which supports the discriminant analysis of principal components (DAPC) with two distinct clusters of CC and NPP dogs. ^[8] A short tandem repeat (satellite) analysis and a count of derived alleles in dogs that were unaffected by the Chernobyl incident. ^[8]

The conclusion was apparent, showing that there was no evidence of radiation-induced characteristics, as there wasn't a higher level of mutation with the NPP population, but there was evidence that directional selection took place with the NPP and CC populations, as they regulate the cell cycle and their response to DNA damage. ^[8] Despite these accomplishments, this experiment didn't find the cause of differentiation between these populations, and further research needs to be done to see if the differences are due to environmental exposures.^[8]

The dogs are at risk of facing aggression from local wildlife, namely packs of wolves. This drives them out of the surrounding forests and closer to power plants as well as human contact. These aggressive interactions with wild animals are a source of rabies in the population. ^[10] Their lack of innate survival skills make them reliant on humans and unable to live independently.

Jonathan Turnbull, cultural and environmental geographer of Cambridge University's geography department, documented how guards and workers within the exclusion zone frequently developed relationships with these dogs. Workers build them shelters, provide them with scraps and other leftovers as well as administering basic care like tick removal. In return for the guards' care, the dogs ward off encroaching wolves and provide entertainment along with needed companionship. The Russian invasion of Ukraine which led to the Capture of Chernobyl resulted in over 300 staff on duty at the time being held hostage and the dogs being briefly left without supervision and care. ^[11]

The 2019 documentary film "Fallout Dogs" directed by Julia Oldham follows the activities of stray dogs around the Chernobyl Exclusion Zone. Oldham, a multimedia artist known for exploring relationship between nature and technology, ^[12] features a local translator and tour guide of the Exclusion Zone in the film and highlighted the local's personal efforts to care for the dogs by way of feeding and interacting with them frequently. ^[13]

As of 13th October 2025, Clean Future Fund employees noticed a change in fur color, with some of the dogs having a blue-tint to their fur; three have been observed thus far. The spokesperson for the CFF stated that they believe that the dogs may have gotten into a chemical, but due to these dogs being able to recognize CFF workers by their uniform, they have evaded capture.^{[14] [15]} The Veterinary Medical Director for the Dogs of Chernobyl program with the Clean Futures Fund, Dr. Jennifer Betz, has made public a heavily supported theory on 31st October 2025, as these "blue dogs of Chernobyl" were spotted near a porta-potty, leading researchers to believe the dogs have been rolling in a blue chemical from the porta-potty, which resulted in the blue coloration, clarifying that this coloration has no relation to genetic mutation. ^[16]

Since 2017, the Clean Futures Fund has implemented annual clinics in the Chernobyl exclusion zone to vaccinate, spay, and neuter the dogs of Chernobyl. This effort is made to reduce the risk of rabies passing to workers and tourists, to decrease the population size of the dogs, and to minimize the suffering that the dogs experience.^[10] The dogs in the zone are able to recognize the uniforms of CFF personnel and often avoid capture. For this reason, the CFF changes the color of their uniforms every year in order to vaccinate, spay, and neuter the dogs.^[17]

In October 2022, Clean Futures Fund visited and sterilized 130 of the newly estimated 700 dogs. During a return visit in June, it was discovered that no puppies had been produced in the several months since the visit in October.^{[18] [10]}

• Chernobyl, Ukraine
• Animal welfare and rights in Ukraine
• Street dogs
• Dogs in the Soviet Union

• CS1 maint: article number as page number
• Articles with short description
• Short description is different from Wikidata