Dogs have been shaped in the course of domestication based on human needs so that many of their characteristics are different from those of their wild ancestors. They reach sexual maturity earlier, their behaviour, however, stays juvenile for a longer time, they accept training and a subordinate role to humans. We have bred them so that they have lost the caution which is typical for wolves and have gained many different physical characteristics. Many of those characteristics have reduced the dogs’ survival capability in the wild. Intrusion of dog genes into the wolf population can therefore have a negative impact on wolves. The smaller the wolf population, the bigger the impact of that negative effect, even when hybridisation events are rare.
As wolf-dog hybrids (for short: hybrids) are less adapted to a life in the wild than wolves, and because they possibly have a reduced level of caution, the potential for conflicts with humans is higher than in wolves. Therefore, it is possible that hybrids might attack livestock more often or come close to settlements more often than wolves. This does not have to happen necessarily, but it is possible and causes fears in many people. However, there is no indication for free-ranging hybrids being more dangerous for people than wolves (L. Boitani, pers. comm.).
Legal status of hybrids
The first four hybrid generations are on the same protection level like wolves. This is due to the EU Regulation (EC) no. 1497/2003 for the change of EU Regulation (EC) no. 338/97 of the commission of the council for the protection of species of wild fauna and flora by regulating trade. Article 10 of the explanation of the interpretation of the annexes reads as follows:
“Hybrid animals that have in their previous four generations of the lineage one or more specimens of species included in Annexes A or B shall be subject to the provisions of this Regulation just as if they were full species, even if the hybrid concerned is not specifically included in the Annexes.”
The wolf is listed in annex A of the above mentioned regulation and is therefore a strictly protected species according to §7 section 2 no. 14 BNatSchG (German Federal Nature Conservation Act). Consequently, hybrids are subject to that protection status as well.
Accordingly, it is not allowed to shoot hybrids, as is allowed for dogs, in the hunting context. A legal exception permit is required in order to remove hybrids from the wild. From the species conservation perspective, this is important because otherwise the danger arises that wolves could be shot as presumed hybrids.
From the perspective of international species conservation, hybridisation between wild animals and their domesticated forms, in this case wolves and dogs, are explicitly undesirable and should be avoided under all circumstances. In case hybridisation has already taken place, all necessary measures are to be taken in order to avoid further distribution of dog genes in the wolf population. Hybrids should be removed from the wild as soon as possible.
In the manifesto on the conservation of the wolf, published by the IUCN Species Survival Commission Wolf Specialist Group and the LCIE "Manifesto for large carnivore conservation in Europe", hybridisation between wolves and dogs is clearly declined and considered harmful for the conservation of the species wolf due to possibly emerging negative effects. The signatories of the Bern Convention, including Germany, are therefore asked in Recommendation no. 173 (2014) to make sure that verified wolf-dog hybrids are removed from wild wolf populations.
Experiences from Germany
The development of the wolf population in Germany has a notably positive trend. Despite this, it cannot be ruled out that the population could be negatively affected by cases of hybridisation with dogs. In Neustadt/Spree, the first and - until 2017 - only case of hybridisation between a female wolf and a male dog took place as early as 2003. Six pups that were phenotypically different from wolves were detected in the area in autumn 2003.
Only four of these pups were still alive in January 2004. The female wolf and one pup were successfully caught as part of the wolf management measures in Saxony. The female wolf was equipped with a radio collar and released to the wild. The male pup was transferred to an enclosure in the Bavarian Forest National Park. Two weeks later, another pup, this time a female, was caught with a foot snare. This pup was brought to the enclosure as well. The two remaining pups suddenly disappeared without a trace in February 2004.
The hybrid distinctly differed from wolves in terms of their morphological and physiological characteristics as well as their behaviour. They were considerably smaller with less body weight and had substantially smaller canine teeth. The males became sexually mature with eight months of age (wolves become sexually mature only with about 22 months). The pups’ hybrid status was genetically confirmed.
From the beginning, the captured hybrids showed signs of hospitalism and always used the same paths through the enclosure. They increased the speed of their running of circles and eight-shapes when humans approached the enclosure. The enclosure was not open for visitors. Even after months, the hybrids showed no signs of familiarisation. Obviously, captivity was permanently stressful for the hybrids that have been raised in the wild and captured with nine months of age. Within one year, both animals were seriously injured by the wolves kept in the neighbouring enclosures so that the hybrids had to be euthanized.
Another case of hybridisation between a female wolf and a dog became apparent in October 2017. The female wolf in the Gotha-Ohrdruf military training area in Thuringia that had been territorial since May 2014, had bred with a male dog in the absence of a male wolf in spring 2017 and subsequently gave birth to hybrid pups. The case was detected as late as October 2017, when 6 hybrid pups where photographed at the military training area. As the animals had a black and grey colour and therefore obviously differed phenotypically from European wolves, their hybrid status was initially confirmed on the basis of their visual appearance only. The Senckenberg Research Institute, Research Station Gelnhausen, confirmed this assessment some time later, as no genetic samples were available from the pups until later. Until autumn, there were only kill samples available from domestic animals killed by the mother without participation of the pups.
According to the Thuringia wolf management plan, hybrids have to be removed from the wild. As a consequence, the Thuringian Ministry of Environment, Energy and Conservation decided that the hybrids should be removed from the wild until early February, 2018. Removing the hybrids as soon as possible is important, as it is possible that they are early to sexual maturity, usually within the first year of their lives. At the beginning, attempts to capture the hybrids alive were made. From January 2018 on, lethal removal was pushed forward as well. In late March 2018, the ministry reported that three of the four pups that had been detected in the area had been killed (two males, one female) over the winter. The fourth hybrid, a male, was in its mother’s territory until April 2019 and was subsequently shot. Shortly after, there were first evidences of a male wolf that had migrated into the area. However, it turned out in the summer of 2019 that the female had mated with her two-year-old son shortly before the male's arrival in March 2019, and given birth to another hybrid litter. In this case, the pups were hybrids of the first backcross generation. An exception permit to remove them from the wild was issued for those pups, too. As all attempts to catch them alive failed despite intensive efforts, the strategy was changed and three pups were lethally removed in February 2020. In May 2020, one hybrid pup still remained in the area. Since the male wolf has migrated into the area the female paired up with him and in May 2020 gave birth to wolf pups for the first time.
In summer 2022 another case of hybridisation between a female wolf and a domestic dog took place in Thuringia, in the territory Zella-Rhön which is situated very close to the border with Hesse and Bavaria. Five pups were confirmed, three of which have been lethally removed until the end of the year.
Also in Brandenburg a case of hybridisation was confirmed in summer of 2022. In the territory Rautenkranz near the Polish Border a male of unknown origin, for which genetic analyses using the SNP-method stated an approximate degree of hybridisation at F2- generation level, mated in the 2022 breeding season with a female wolf. Four pups could be assigned to the pair, of which a female pup died in a traffic accident in October 2022. Using a SNP analysis following Harmoinen et al. (2021) the pups could be assigned to the 2. backcross generation to wolf. For the male and the pups a permit for removal was issued by the nature conservation authorities of Brandenburg.