Northernmost record of reproduction of the expanding golden jackal population

Golden jackal (Canis aureus) is expanding north in Europe. So far, its reproduction has rarely been reported in the expansion area. In this paper, we describe the first cases of reproduction of golden jackal from northern Poland, 500 km north from previously reported records. In summer 2015 and 2017, golden jackal juveniles (four and five individuals, respectively) sightings were recorded near Kwidzyn in Vistula river valley, where jackals have been observed repeatedly since 2015. These are the northernmost records of golden jackal reproduction in Europe. Since 2015, golden jackal was recorded in 15 locations in different parts of Poland, usually in the vicinity of larger rivers in mosaic habitats. The reproduction records suggest local establishment of population with predicted population increase and further expansion. First observation and record of reproduction in the same year suggest that expansion of golden jackal in Poland took place earlier and was not recorded, probably due to lack of knowledge on the species and failure to recognize its individuals.

Range shift is one of the relatively well-understood responses of organisms to climate change (Williams and Blois 2018). It has evolved to maximize species fitness in a particular ecological niche and match their spatial shifts (MacArthur 1972;Sexton et al. 2009). The process of range shift includes four key stages: (1) emigration: individuals leave natal location; (2) movement: transfer of individuals away from original location; (3) establishment: the ability of individuals to reproduce and found new populations; and (4) proliferation: the growth of established populations to become more than self-sustaining and able to further spread (Estrada et al. 2016). Successful range shift and population establishment require similar or substitutable resources in the new environment, including food and shelter in the short term, and mate availability in the long term (Šálek et al. 2014;Hovick et al. 2016;Mukherjee et al. 2018).
The golden jackal (Canis aureus) is one of the southern carnivore species, that after population decline and recovery, not only recolonized its previous range, but also is expanding in Europe (Arnold et al. 2012;Trouwborst et al. 2015;Kusza et al. 2019). In recent years, new records of golden jackal in Baltics, Belarus, Czech Republic, Germany, Poland, etc. were reported (Trouwborst et al. 2015;Kowalczyk et al. 2015;Grichik et al. 2018;Jirků et al. 2018). The population is probably in the movement stage as population establishment including reproduction is rarely reported (Pyšková et al. 2016;Jirků et al. 2018;Lanszki et al. 2018). Golden jackals may disperse rapidly and over long distances, even across human-dominated landscapes (Lanszki et al. 2018). In expanding populations, species occurrence and reproduction in new areas are probably observed and reported with some delay, related to the low probability of observation being a result of low densities at the beginning of colonisation, lack of knowledge on the species and the likelihood of confusion with other animals (McKelvey et al. 2008).
In this paper, we describe the first evidence of golden jackal reproduction in Poland, the northernmost ever found in Europe, based on repeated observations of juvenile individuals. We also update the occurrence records of golden jackal in Poland. The observations of juvenile jackals were collected by experienced hunters and foresters during field visits and occasionally confirmed by photo-documentation. Other records of jackal presence from Poland were based on necropsy and morphological (including connate pads of the medial toes of fore and hind limbs) and genetic investigation of dead individuals conducted in the Mammal Research Institute, Polish Academy of Sciences (for details see Kowalczyk et al. 2015), or photographs and videos received. Jackals on photos and videos were identified on the basis of the features such as coat coloration, body size and proportions, and the tail length.
In late August 2015, a golden jackal family including 2 adults and 4 juveniles were observed at dusk on the fields near Biała Góra village in Kwidzyn area in N Poland (Table 1; Fig. 1). The same animals were seen several   Table 2 times by hunters and foresters in the area in late summer. In autumn 2015, 2 adults and 3 juveniles were observed and heard when howling. Single individuals were seen repeatedly during the next years. In August 2017, five juveniles were seen emerging on the terrain road (Table 1, Fig. 2). Between July 2015 and July 2019, 15 confirmed records of golden jackal in Poland were reported ( Fig. 1 and Table 2). There were seven dead individuals (six genetically confirmed at MRI PAS) and eight observations (seven confirmed by photos or video). All the observed individuals or group members had size and coat coloration typical for the golden jackal. Majority of the observations were in the vicinity of larger river valleys, seashores or lakes in mosaic habitats including meadows, marshes, agriculture, waste and woodlands.
Since the first case of golden jackal presence in Poland in 2015, very limited number of observations or dead individuals had been recorded (Kowalczyk et al. 2015, this study). This indicates movement phase and exploration by migratory individuals rather than establishment of the population. However, first records of reproduction from the same year as the first observation of the species in Poland indicate earlier than reported expansion and local population establishment far to the north from its original distribution range. The delay in species expansion discovery is probably related to the lack of knowledge on the animal and failure to recognize individuals of this new species. Since the first observation of golden jackal, media in Poland reported almost every new record of the species. This led to the increasing number of species records reported by public; however, only very few cases turned out to be golden jackals. Majority of them were foxes, often suffering from scabies, dogs or wolves (R. Kowalczyk, personal comm). However, increasing knowledge on the species brings increasing number of confirmed observations. The scenario is similar to the expansion of raccoon dogs in Poland during the 1950s, when very fast spread and establishment of population was recorded, exceeding the biological capacity of the species (Nowak and Pielowski 1964;Kowalczyk et al. 2009;Kauhala and Kowalczyk 2011). Thus, expansion and saturation of the environment were probably slower, and discovered with some delay, when growing abundance of the species and increasing knowledge allowed for more frequent species recording and rapid increase in the amount of data on species occurrence.
Despite several unconfirmed breeding records outside its continuous European range (Trouwborst et al. 2015), the northernmost reproduction of golden jackal so far was confirmed in northern Czech Republic (Jirků et al. 2018). Reproduction of golden jackals 500 km north from the previously reported location indicates fast expansion and local establishment of the population. In the Kwidzyn area, where the reproduction was recorded, repeated observations of single individuals and groups of jackals and howling were reported. Thus, local establishment of population and reproduction is associated with more frequent signs of animal presence and territorial behavior (howling).
The majority of observations of jackals in Poland are in lowlands, near river valleys and wetlands, which are typical habitats of golden jackal (Trbojević et al. 2018). River valleys may also play a role of migratory corridors facilitating expansion in human-dominated landscapes such as in Poland (Huck et al. 2010), offering abundant food resources during migration, for this vole-specialized carnivore (Lanszki and Heltai 2002;Penezić and Ćirović 2015).
In 2017, golden jackal obtained in Poland the legal status of game species with the hunting season from 1st August to the end of February with delayed implementation until 2019 (Regulation of the Ministry of Environment, 1st August 2017). However, the low number of species records puts the hunting of jackals into question in the light of the status of golden jackal in European legislation (Trouwborst et al. 2015;Sillero-Zubiri et al. 2004). Golden jackal is listed in Habitats Directive Annex V (Council Directive 92/43/EEC of 21 May 1992), which covers animal species of community interest whose exploitation may be subject to management measures; however, according to the Directive provisions, it should also be maintained at favorable conservation status. It rather indicates need of species protection, not hunting, at the present state in Poland. It also carries a risk for widely distributed and increasing population of wolf, protected in Poland, with which the golden jackal may be confused. other observers from Poland for providing information of golden jackal observations and photos. We thank Dr. Marta-Kołodziej-Sobocińska, Dariusz Chilecki and Iwona Ruczyńska from Mammal Research Institute PAS for help in jackal necropsies and genetic identification. We also thank Eleanor Stockwell and Kingsley Hunt for reading the manuscript and improving the English two anonymous reviewers for comments that helped to improve the paper.

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Conflict of interest The authors declare that they have no conflict of interest.
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