Is the parti-coloured bat Vespertilio murinus Linnaeus, 1758 a common bat species in Slovenia?

. In the last overview of bats in Slovenia, the parti-coloured bat Vespertilio murinus was one of the rarest species listed. However, in the past few years (June 2005 - April 2013) we have found 98 new locations. In this article, we present new data on mating sites, summer roosts and hibernacula, as well as other chance encounters. Although V. murinus is a permanent part of the bat fauna in Slovenia, it is much more evident during the colder part of the year, when migrating individuals possibly reach their wintering area. We argue that this bat species is much more common in Slovenia and its neighbouring regions than previously assumed.


Introduction
The established range of Vespertilio murinus in Europe stretches from the Pyrenees Mountains, over central Europe to the south of Scandinavia, and towards Russia.Records south of the Alps are rare; the species, however, has been found in the northern part of Italy, Slovenia and throughout the Balkan Peninsula as far as northern Greece (Baagøe 1999, Dietz et al. 2009, Alberdi et al. 2012).In the latest overview of bats in Slovenia (records dating until mid 2005), Zagmajster (2009) reported only on 12 V. murinus sites (13 encounters).On almost one half of these sites (five), male display calls were heard, exact locations established for two males and two females, and three chance encounters made, where sex of the animals was not recorded.Without any exact roost being known, this bat was ranked among the four rarest out of the 28 bat species living in Slovenia (Presetnik et al. 2009a).
In recent years, we regularly heard display calls of V. murinus during ultrasound transect monitoring (Presetnik et al. 2007(Presetnik et al. , 2009b(Presetnik et al. , 2011(Presetnik et al. , 2012)), which encouraged additional research to locate their mating sites.Ultrasound field observations, along with a few discoveries of summer roosts (e.g.Ţibrat 2005Ţibrat , Petrinjak 2010) and hibernacula, as well as additional records of chance encounters of mainly injured or exhausted bats, gave a significantly different picture of the species' distribution and frequency of occurrence in Slovenia, which we present in this paper.

Ultrasound inventarisation
During the establishment of the national bat monitoring scheme, several foot transect counts using ultrasound detectors were selected (Presetnik et al. 2007, Presetnik & Podgorelec 2008).Among them, a transect near the hamlet of Leskova dolina in the southern part of Slovenia close to Mount Sneţnik (at approximately 850 m a. s. l.) was selected, with the main purpose being monitoring of V. murinus, since we had previously heard the bat's characteristic echolocation calls (Schaub & Schnitzler 2007) and social calls (Ahlén & Baagøe 1999) there.
On this particular transect, we repeated field observations of V. murinus in almost each consecutive autumn, which prompted additional ultrasound inventarisation, a pilot study in 2009, and more intensive research in 2011 and 2012.The method used was slow driving by car (approximately 20 km/h) while listening with unaided ears for the bat's social calls, and with an ultrasound detector (Pettersson D240x) for its echolocation calls.We recorded all bat calls with a digital recorder (Marantz PMD 670) and later analysed the data with the BatSound 4.0 program (Pettersson Elektronik).Firstly, we selected transects in the vicinity of V. murinus known locations (Presetnik et al. 2009a), then in similar environments in some other parts of Slovenia, including the capital city of Ljubljana.Most transects were carried out in October and one in November, and they usually started approximately 1-1.5 hours after sunset and lasted, with one exception, for less than 3 hours.Additionally, we also recorded some advertisement or echolocation calls of V. murinus on a few other occasions.

Roosts and chance encounters
During the period between mid 2005 and mid April 2013, many members of the public informed the SDPVN -Slovenian Association for Bat Research and Conservation on finds of injured, exhausted or strayed bats (e.g.Podgorelec 2011), which we will address as »chance encounters«, or on sightings of groups of bat in various environments, and when we checked these finds, some turned out to be V. murinus.If possible, we measured the bat's mass (0.5 g accuracy), the length of its forearm (0.1 mm accuracy), and determined its sex and reproduction status.

Autumn ultrasound inventarisation and other ultrasound observations
During the national monitoring ultrasound surveys on the »Leskova Dolina« transect, we heard advertisement calls of V. murinus in five out of six autumn counts, and echolocation calls during one out of six summer counts (App.1).During nine car transect surveys, we covered slightly over 500 km (Tab. 1, Fig. 1); we recorded V. murinus on 59 occasions (57 new locations and two repeated locations) and heard social calls on 43 of them (App.1).The number of locations per car transect ranged from zero (three transects) to 21 (Tab.1).On six transects with V. murinus recorded, the average number of recordings per kilometre was 0.21 (range: 0.09-0.39).On car transects, 76% of bat observations concerned V. murinus.During other ultrasound transect surveys conducted on foot and during other field inventarisations, we recorded V. murinus on 21 occasions in 14 locations, and heard social calls 15 times (Fig. 1, App. 1).
Altogether, we heard V. murinus on 86 occasions in 72 new locations and once in a previously known location (Fig. 1, App. 1).The locations ranged from between 150 to 1,100 m a. s. l.The bats were predominantly observed in small and large settlements with at least one street light (39.7% of locations), though most observations occurred on the edge of a settlement, where lights were not present or illumination was dim, and a forest edge was close by.Smaller settlements -hamlets without street illumination, usually located in forest clearings or close to forest edges -accounted for 19.2% of locations.Locations on forest edges (e.g.roads in forests) accounted for 17.8% of locations, forest clearings that contained a building (e.g.forester's hut, hunting hut or some other sort of building) accounted for 16.4% locations; a further 5.5% of locations were in forest clearings without any building, while one location (1.4%) was on the bank of a large river.

Records of summer roosts and hibernacula
On 6. 6. 2009, the owners of the Mini Hotel in the village of Vincarje near Škofja Loka (Fig. 1, location 1) noticed many bats emerging in the evening from behind the outer wooden panelling of a two-storey building.On 10. 6., 47 bats emerged, while on 14. 6., at least 50 were recorded, and since all three caught bats were adult V. murinus males (App.2), we apparently observed an exclusively male group.The summer roost of the second male group was located behind a closet standing on the balcony of the fourth floor of a block of flats (Bezje 4) in the village of Kranjska Gora (Fig. 1, location 2) and was observed on 19. 7. 2010 (Petrinjak 2010).The colony consisted of 11 animals and from the 10 measured all were males (App.2).Another summer observation (1. 8. 2005) was reported by Presetnik (2007) from the attic of the Fala Mansion (Fig. 1, location 3), where an unsexed individual was hanging close to the apex of the roof.
On 15. 2. 2011, a hibernaculum of V. murinus was discovered in the entrance section of the cave known as Planinska jama (Fig. 1, location 4), as four bats (two adult males, App. 2) were found to be hiding separately in shallow crevices among more than a hundred Pipistrellus pipistrellus, at temperatures between 4.4-4.9°C.We found another adult male in a crevice approximately 3 m above the ground and 30 m from the entrance of the cave Huda luknja near Gornji Doliĉ on 9. 2. 2013 at 2.0 °C (Fig. 1, location 5, App. 2).Another bat of unknown sex was hibernating in a warehouse in the village of Spodnja Reĉica near Laško (Fig. 1, location 6) on 22. 1. 2013, where discovered upon the shifting of a piece of warehouse equipment.

Chance encounters
From mid 2005 until mid April 2013, 20 other observations of V. murinus were made (Fig. 1).In App. 2 we list details on them, together with details about three animals, the locations of which and dates of their discovery have already been given by Presetnik et al. (2009a).Altogether, out of 18 animals examined by experienced chiropterologists, 13 were males and five females (one nulliparous, three adult and one female whose reproductive status was not assessed).One third of animals were found in December and January, while the second numerical spike was registered in April, when almost one quarter of animals were found.We recorded no injured, exhausted or strayed V. murinus in the June-September period (Fig. 2

Discussion
We have documented records of Vespertilio murinus at 98 new locations in Slovenia ( 72ultrasound observations, 6 roosts, 20 chance encounters; Fig. 1), which is an 8-fold increase in the number of locations for this species in comparison to Zagmajster (2009).However, the change in research methodology had contributed to the sharp increase in the number of locations found.Before our study, autumn ultrasound surveys with adequate equipment were extremely rare, but interestingly, if they were performed, V. murinus was quickly found (Zagmajster 2003).Autumn ultrasound surveys also had an advantage over summer counts, since in autumn, male V. murinus often performed unmistakable display songs.The rarity of ultrasound finds during the summer period (foot surveys Leskova dolina, Most na Soĉi, Kranjska Gora; App. 1) could be a consequence of a) possibly smaller summer population of V. murinus, and/or b) the difficulties to exactly determine their echolocation calls, which can be easily confused with other species (e.g.Nyctalus noctula, N. leisleri, Eptesicus serotinus (Ahlén 1990)).In any case, our autumn inventarisation revealed that V. murinus is, at least in some areas, very common.In fact, during our October and November inventarisations, it was the most frequently recorded species, but as the extent of research was limited, additional research would be necessary to make conclusions as to the abundance of specific bat species.
It is unclear why we frequently heard V. murinus along some car transects and did not record it at all along others, but it could possibly be connected with the weather conditions in which our field research was performed.At least on the evening of »car transect I« (Tab. 1, Fig. 1), when we did not hear V. murinus, the weather changed from high pressure and clear skies of the previous days to low pressure with low cloud cover and heavy fog.
Obviously the same areas were possibly used by V. murinus as mating sites over a span of several years, given that we regularly recorded it in different years at the end of the »Leskova dolina« foot transect in the hamlet of Leskova dolina itself (App.1), as well as on both occasions when we surveyed the hamlet of Šranga (car transects A and B, App. 1).Another sign of site fidelity are the observations of display songs at the forest clearing along the forester's hut at Medvedjek (car transect D), where display songs had actually been observed 11 years earlier (Zagmajster 2003).The apparent mating site fidelity by V. murinus and the easy determination of the species' social calls could be used in the future as a way for its long term monitoring, since Slovenia's current bat monitoring system cannot provide information on population trends for this species (Presetnik et al. 2011(Presetnik et al. , 2012)).
Records regarding the two summer colonies, together with the observation of an individual in the Fala Mansion and the summer ultrasound observations (App. 1, 2) are strong evidence that a permanent population of V. murinus exists in Slovenia.For now, it seems that the summer population is composed mainly of males, since only one observation of a gravid female has been made in the night between 3. and 4. 6. 1994 (Kryštufek & Ĉerveny 1997).
We have to note that in the area of Koĉevski Rog, where this gravid female bat was found, almost no additional inventarisation was made in a similar period, but perhaps this female was late on its migratory journey towards its maternity area in the north.This assumption is based on the fact that all the closest confirmed maternity colonies of V. murinus are situated in the western part of Switzerland, the southern part of Bavaria and the Czech Republic, and that the centre of its maternity area is even further towards NE Europe and Russia, where maternity colonies are formed from May to August (Baagøe 2001).It seems that the situation in Slovenia is similar to the situation in neighbouring Austria, where only male groups or nonreproductive females have been observed during summer (Spitzenberger & Bauer 2001, Guido Reiter in litt.).
The finds of V. murinus hibernating in fissures in caves are also interesting, as they point out at possible natural winter roosts in rock walls.In caves, V. murinus is not usually seen (Rydell & Baagøe 1994), though Hanák et al. (2010) give accounts of bone deposits in rocky fissures covering the period from the late Pleistocene to recent times.The rarity of observations in caves and cliffs could be related to the difficulty of discovering bats hibernating in narrow crevices.In general, the reported observations in Europe show V. murinus hibernating in buildings, where it is usually discovered during their renovation or shifting of a piece of equipment (Rydell & Baagøe 1994), as was also the case in the warehouse in Spodnja Reĉica.Additional hibernacula were probably also close to some locations where we noted injured, exhausted or stray bats (App.2).Dates of these finds are concentrated in the autumn through the winter to mid-spring period and not during the time when pups are born (late June, early July; Baagøe 2001).This suggests that Slovenia is used by male and female V. murinus as a wintering area (finds in December-February) and probably also as an area for its seasonal migration (finds in March-May and October-November).Although not a single out of 8 V. murinus banded in Slovenia has been recovered, possible vagrant parts of the population probably migrate toward the NE of Europe as suggested by band recoveries in neighbouring Austria (Hutterer et al. 2005).
Our research confirmed that V. murinus is a permanent part of the fauna in Slovenia, though it is much more conspicuous during the colder part of the year; possibly also because of seasonal migrations.We expect that some additional autumn research would quickly reveal its presence in most areas of Slovenia and, of course, in its neighbouring regions.