Earliest data on jackal presence on the continent. Data on the historical distribution of the golden jackal in Europe and its primary habitats are scarce. Despite the many new data on the population explosion and the rapid spread of the species across Europe, the main factors for such population expansion remain controversial. The core population/local populations and the routes of dispersal remain insufficiently studied.

Hosey (1982) suggested that the jackal could have reached Europe from the east at the end of the Pleistocene, a hypothesis that appears justified from the zoogeographic viewpoint. Theoretically, the jackal could penetrate in Eastern Europe in two ways, that correspond to the potential paths at the end of Pleistocene and Holocene: along the northern Black Sea coast and through the Bosporus (Spassov 1989). The opening of the Bosporus took place 7600 cal BP or, more probably, 9300 cal BP (Yanchilina et al. 2017).

The area of distribution of the European subspecies Canis aureus moreoticus (Geoffroy, 1835) during the first half of 20^th century occupies a relatively vast territory from the Balkans, which is the initial European territory, up to Anatolia and Caucasus. There is no significant difference in the colouration pattern and other features across the various subpopulations living in this area (Pocock 1938, Heptner et al. 1967, Demeter and Spassov 1993). Despite several old and relatively recent statements about Late Pleistocene presence of the golden jackal in Europe, there are no fossil records of Canis aureus found on the continent (Demeter and Spassov 1993, Lapini et al. 2011). The Pleistocene climate may have been inappropriate for this species (see below) and there are no data on fossil records of C. aureus in the proximity of the eastern and south-east European territories between the end of the Pleistocene and the beginning of the Holocene: according to Vereshchagin (1959) and Baryshnikov (1986), there are no confirmed remains of C. aureus from the Pleistocene of the Caucasus and Transcaucasian Region and that the species possibly reached this area rather recently, in the Middle Holocene. Several doubts, regarding the presence of the jackals in the Holocene of Europe, have been expressed. These concerns, however, were based on problematic remains and turned out to be erroneous (see Spassov 1989). The available remains reported as “subfossil jackals” from Bulgaria were also revised years ago. They clearly belong to dogs (Spassov 1989). More recently, this question was raised again by Sommer and Benecke (2005), who cited Jullien (1968) and Tranier (1973) reporting that the species was found in the Neolithic in Greece. These claims were based, again, on unsure, scarce bone remains which have not been described, compared nor figured. In the last decades, one of the authors (N. S.) observed hundreds of skull remains of Canis from many Neolithic to Medieval sites in Bulgaria (see Material and methods). No jackals were determined there. All of this suggests that, until now, there is no proof about discovered fossil or subfossil remains of jackals in Europe and that the claim (Sommer and Benecke 2005) about the species presence in the Holocene of Greece (widely cited, e.g. Zachos et al. 2009, Rutkowski et al. 2015, Trouwborst et al. 2015, Krofel et al. 2017, Lanszki et al. 2018) is more than doubtful, as it is not based on surely determined remains.

It possibly penetrated in the Early Holocene and lived as a rear animal without economic value for humans and has almost never been hunted (that is why it has not been found yet); as a good swimmer, it could penetrate from the east even in historical times (Spassov 1989). It could have been introduced most probably in post-antiquity as a pet animal (Keller 1909). For the moment, in the absence of evidence, this appears to be a possible hypothesis.

The first record of a jackal in Europe (the south-eastern and eastern parts of the continent) dates back to the Middle Ages. The earliest reliable historical data are from the end of the 14^thcentury (the vicinity of Sofia), from Turkish chronicles, during the siege of the town (Gueorguiev 1983). There is an anecdotal story about Venetian sailors who introduced jackals in the 15^thcentury on the Dalmatian coast from North Africa (Kühn 1935, Milenković 1987). This story which, as it seems, has caused diplomatic complications at that time, finds confirmation in an official letter between the leaders of Zara\Zadar and Venice, which is stored in the national archives in the Zadar City (Miklós Heltai in lit.). The North African origin is not supported by taxonomic studies (Kryštufek and Tvrtkovic 1990), but it is interesting to note that the Dalmatian local population is more distant morphologically and genetically from the other Balkan ones (Kryštufek and Tvrtkovic 1990, Fabbri et al. 2014). For Ukraine, historical data exist from the so-called Cossack Era (16^th-18^thcentury) (Zagorodniuk 2014).

History of jackal distribution from the end of the 19^th until the 1930s of the 20^th century (Fig. 2). In Europe, the jackal was mainly distributed within the Balkans (Blasius 1857, Atanassov 1953, Pomakov 1981, Milenković 1987, Spassov 1989, Demeter and Spassov 1993, Kryštufek et al. 1997, Giannatos et al. 2005). The more stable local populations were presented in the Thracian Region (Northern Thrace in Bulgaria, Eastern Aegean Thrace in Greece and Western Thrace in European Turkey), Dalmatia and Peloponnesus, with pulsations/expansions to the west/northwest during favourable periods: it existed on the Bulgarian Black sea coast and occasionally reached West & North Bulgaria and possibly even North Serbia (Atanassov 1953). The population occurred mainly on the southern coast, covering the territory between the Marmara and Aegean Seas (from Istanbul to Chalkidiki, interrupted along the western Greek coast and Peloponnese); to the north, the distribution extended between the Eastern Rhodope Mts., the Sakar hills and the Strandja foothills from the Bulgarian and Turkish Territories, as it continued northeast along the Black Sea coast of Bulgaria to Varna and even to the Romanian border; to the west through mountainous border territories from South-Western Bulgaria to the foothills between today's Republic of North Macedonia and northern Greece.

On the Adriatic coast, there were fragmented small subpopulations (apparently with temporary connections between them): from the Greek coast south of Ioannina to small spots along the Albanian coast and, from there, to the Dalmatian coastal area (including the Pelješac Peninsula and Korčula Island).

In Romania, the jackal was also an occasional visitor from Bulgaria, crossing the frozen Danube River during severe winters (Vasiliu 1961, Vasiliu and Şova 1968). It was reported for the first time in this period in 1929 in Wallachia, in front of the town of Lom (in North-Western Bulgaria), but in the 1920s, it also appeared in Romanian Dobrudja (Calinescu 1930, Atanassov 1953). A small localised population existed in Hungary at the beginning of the 20^th century (Ehik 1938, Demeter 1984). From there, it seemed to have disappeared in the early 1940s.

In Eastern Europe, the species occasionally penetrated from the Caucasus to the Don River estuary (Musabekov et al. 2016).

There are two very different tendencies of the population dynamics which are treated in this article as two periods: from the middle of the 20^th century till the 1980s, a great reduction in the population was observed. It was followed by the beginning of a population expansion.

History of jackal distribution from the second half of the 1950s until the beginning of 1960s: population minimum (Fig. 3). The jackal population shrunk, the peripheral small populations gradually disappearing from Hungary (unconfirmed individual records from 50s: Tóth et al. 2009), Romania, Republic of North Macedonia, Serbia (except for some small isolated spots) and Bosnia. In fact, in Bulgaria, the reduction of the species numbers was noticed long before this (Atanassov 1953, Milenković 1987, Demeter and Spassov 1993, Kryštufek et al. 1997). In the 1950s, jackals were reported in the southern part of Romania and in north-eastern Romania near Piatra Neamt and Focsani (Banea et al. 2012). These cases were probably related to occasional dispersals from Bulgaria. It disappeared in many areas during the 1960s because of habitat loss and poisoned bait (Spassov 1989). It remained in localised subpopulations within the Balkans, which we can call basal (core) populations. From these population nuclei, in the late 1960s and most notably in the 1970s, stabilisation and expansion to the north and the west began to occur.

The core populations could be defined as follows: 1. Strandja coastal area of Bulgaria and Turkey (probably also some areas in E. Rhodope-Sakar Mts.) (Pomakov 1981, Spassov 1989); 2. Fragmented Adriatic population, mainly in Dalmatia (in Slovenia from the early 1950s, most likely entering from Croatia, however, disappearing quickly afterwards) (Demeter and Spassov 1993, Milenković 1987, Kryštufek et al. 1997); 3. Strimon-Chalkidiki Region (skeletal population, possibly including vagrants around Dojran lake); 4. Peloponnese population (isolated no later than the end of the 19^th century).

Most important in relation to the further expansion of the species are the first two core populations. The astonishingly high current number, over 30,000 individuals (Stoyanov 2013) and high-density areas, 5.66 to 7.08 territorial groups per 10 km² (Acosta-Pankov et al. 2018), represent additional signs that the territory of Bulgaria is related to the core area of the population dispersal in Europe.

Beginning of the expansion on the continent: population explosion of the Strandja and the Adriatic core populations (Fig. 4). Our distribution analysis showed that the most powerful expansion of the jackal began from the Strandja core population and is continuing to the present time.

Bulgaria: In the late 1960s and early 1970s, after poison bait was banned and the protection of the species occurred (in 1962), the expansion began to the north (along the Bulgarian Black Sea coast) and to the west (in the Thracian lowlands and to the west of south Dobrudja) avoiding the high mountains (Pomakov 1981, Spassov 1989, Demeter and Spassov 1993). From the Strandja-Sakar region, the expansion increased possibly also to the south, influencing the distribution of the population in Eastern Thrace, Turkey (there is no reliable data for this period) and Western Thrace (judging from the map of distribution of the species in Greece: Giannatos et al. 2005). In the first half of the 1980s (some data indicate individual vagrants before this time: Sofia plain), the jackal reached Western Bulgaria excluding the border mountainous territories and south-western parts, where large mountain massifs occur (Genov and Wassilev 1989).

Romania: In the early 1970s, the jackal reached Romanian Dobrudja again (Kryštufek et al. 1997). In 1970, footprints were observed in Romania at the Humor Monastery’s hunting terrain and two jackals were hunted near Voronet (Bucovina); between 1971 and 1975, jackals were registered in the Buzau County in Dedulesti and Stefanesti near Bucharest (Angelescu 2004).

Serbia, Hungary and Slovakia: The species apparently spread westwards, reaching these countries through the lower Danube River plain, coming mainly from Bulgaria, but also from Romania. In the 1980s, the Romanian population expanded to the west and north, from where it reached again, in the early 1980s, Serbia (some individual records exist from the late 70s: Milenković 1987) and Hungary (Demeter 1984, Kryštufek et al. 1997, Tóth et al. 2009). It reached Slovakia in 1989 (Arnold et al. 2011). Markov et al. (2018) found a low epigenetic diversity of the jackal populations from Bulgaria and Serbia to Hungary. This indicates that the long-distance expansion from Bulgaria to Hungary is very recent and has started from a small population within a limited region.

Republic of North Macedonia: In 1989, the species was registered in the north-western part of the country (Kryštufek and Petkovski 1990), apparently coming from Serbia. Entering from Bulgaria was a much more difficult occurrence because of the low population density of jackals (until today) in South-Eastern Bulgaria owing to the unfavourable conditions in the border mountain areas.

The combination of several factors (Spassov 1989) could explain the explosion of the Bulgarian population after the 1960s, which was especially important for the further dispersal of the species in Europe: 1. The prohibition of poisoned bait and the temporary protection of the species in 1962; 2. In the 1970/80s, the hunting/farming in Bulgaria was amongst the best in Europe; fallow deer and roe deer fawns and wild game carcasses represented abundant additional food; 3. The well-developed free sheep-breeding (dead animals represent additional food); 4. The intensive plantations of pine forests in unfavourable areas where they cannot develop: creation of a widespread mosaic of impassable shrubs (shelters); 5. The wolf was still missing in the 1970s and the first half of the 1980s from the territories invaded at this time by the jackal (see: Spiridonov and Spassov 1985).

In the 1980s, probably from the Dalmatian core population (Kryštufek and Tvrtkovic 1990, Kryštufek et al. 1997), some individuals reached Northern Italy (1985) (Lapini and Perco 1988), Slovenia (1985) (Kryštufek et al. 1997) and Austria (1988) (Hoi-Leitner and Kraus 1989). Judging from the growth of the population on the Dalmatian Adriatic coast, the expansion probably reached Albania (see the map of the distribution in Kryštufek et al. 1997), where the status of the species is still cryptic and the population is not abundant (Giannatos 2004, Arnold et al. 2011). Genetic analysis confirms that the Italian population originates from Dalmatia and from Slavonia simultaneously (Fabbri et al. 2014), where the population comes from Bulgaria, via Romania and Serbia (Banea et al. 2012). The Austrian population (possibly also the Slovenian one) may have mixed origins (from the Dalmatian, but also from the Strandja core population, through Serbia): an Austrian vagrant jackal is genetically indistinguishable from the Serbian animals regarding both mtDNA and microsatellites (Kusza et al. 2018). This is interesting, because it has been assumed that the jackals found in Italy, Slovenia and Austria originate from the Istria Peninsula and North-Western Croatia (Kryštufek et al. 1997).

Continuance of the expansion from the end of the 20^th until the beginning of the 21^th century: (Fig. 5). In this last period, there are dense populations of the jackal throughout the main territory of Bulgaria and Serbia, practically all the Wallachian Plain in Romania and northwards and westwards to regions of Europe where it has never occurred naturally, such as Germany (1996) and the Czech Republic (2006) (Arnold et al. 2011). Vagrant specimens have extended to Switzerland and the Baltic Region and it was reported for Estonia in 2013, the Netherlands (2015) and Denmark (2016) (see: Pyšková et al. 2016). As noted above, the population genetic research shows that the jackals from Italy, Slovenia and Austria have mixed origins from Dalmatia and Slavonia (Kusza et al. 2018) (in Slavonia, jackals likely have SE Balkan origin). From Romania, the species reaches Ukraine: the first record has been reported in 1998 for the Danube River Delta (Odessa Region). From there, the most powerful wave of dispersal was directed to the north, in the Polesie Region and recently from this region, most probably the jackal has reached Poland, Belarus, Lithuania and Estonia at the beginning of this century. In the first decade of our century, the jackals, originating from SE Europe, have reached not only Western Europe but have migrated to the east, reaching the border with Russia (Zagorodniuk 2014). The Transcaucasian population appears to be expanding similarly in the late 20^th century, reaching, at the 20^th/21^st century, the eastern parts of the North Caucasus and the Saratov Region, also entering Russia from there. At the beginning of the 21^st century, this population has reached to the west the Ciscaucasia regions of Stavropol and Krasnodar in Russia (Musabekov et al. 2016). Thus, in recent times, the European population, expanding in the late 1960s from the Strandja core population, has made contact with the Caucasian (Trans-Caucasian) population of C. a. moreoticus, at the border between Ukraine and Russia. The genetic structure of the studied Lithuanian sample suggests that part of the Baltic jackals originate, as could be expected, from the population from South-Eastern Europe, while others (from the Estonian sample) originate from the Caucasus Region (Rutkowski et al. 2015), supporting the statement about a Caucasian (Transcaucasian) expansion in recent times.