Distribution of pygmy field mouse Apodemus uralensis (Pallas, 1811) population in Poland: review of the studies and new data

Northern and western border of pygmy field mouse Apodemus uralensis population area passes through southern Poland. First sites of the species have been discovered in the '50 of the 20th century. Since then, a total of 79 sites has been found. Latest research revise data concerning the occurrence borders of pygmy field mouse. Three out of four newly found stations are located in the western part of the country, north-west from the hitherto known sites of the species.

Pygmy field mouse Apodemus uralensis (Pallas, 1811) is one of the hardest to identify rodents in the Muridae family.Morphologically, it most resembles a wood mouse Apodemus sylvaticus L. (Kowalski & Ruprecht 1984).It is a palearctic species, which occurrence range spans across central Europe: Czech Republic, Slovakia, eastern Austria, Hungary, Romania, Bulgaria and Ukraine (Storch 1999, Vohralik 2002, Zima & Andera 1996, Zagorodniuk 2005).The rodent can also be found in the northern regions of Lithuania, in Latvia and Estonia (Storch 1999, Juskaitis 1999).In the European part of pygmy field mouse range the population is unevenly distributed.In central Europe, a clustered population is located in Slovakia (Storch 1999).Outside Europe, its occurrence range reaches out to western Kazachstan, north-eastern China and Mongolia (Storch 1999).In Carpathian Mountains this mouse can be found up to 1400 m over sea level (Krystufek et al. 2008).This species prefers dry, unforested and agriculturally-used environments (Glazaczow 1984).
Pygmy field mouse has been included in IUCN Red List of Threatened Species, in the Least Concern category.It is due to the scarce data on species' population (Krystufek et al. 2008).
In Poland, this species is known from Jaskinia Dużej Sowy fossils, dated back to late holocene (Kowalski 1989).Northern border of the mouse's range passes through southern Poland (Vohralik 2002).However, its exact course is not known.The rodent's occurrence range includes a south-eastern stretch of the country, including highlands of southern Poland and a part of Carpathian Mountains.The highest locality in Poland is 1000 m over sea level (Haitlinger 1990).It is a relatively new species in the countries' mammals' fauna.The oldest contemporary site in Poland is dated back to 1955 (Ruprecht 1983).Since then fragmentary data concerning new stations spread across southern Poland has been found.
The aim of the paper is to analyze the spreading of pygmy field mouse across the country, from the first confirmations of the species to the most recent data, as well as relating Polish area changes to the European span of the species (Storch 1999).The studies on placement and increase of the pygmy field mouse occurrence area in the country have been based on literature data analysis, as well as research.The research was based on analysis of birds of prey's pellet material (Table 1).Data on confirmed presence of the rodent was analysed in five timeframes: 1955-1960, 1961-1970, 1971-1981, 1982-1992, 1993-2004.A geographical localisation (macroregion) has also been added to each station (Kondracki 2000).For each station, there is a UTM (Universal Transverse of Mercator) grid square, with a side of 10 km.The source of information on the mouse's stations has been described as following: C -capture, P -pellets.
Total surface occupied by pygmy field mouse population has been calculated by adding the UTM squares where the species was confirmed.For the percentage of the country's surface occupied by the species' population, inland waters have been excluded from the total surface, amounting to 309 074 km2.
Confirmation of the rodent in this study is based on both descriptive features and measurements of skulls (Ruprecht 1979(Ruprecht , 1993)).The most practically useful taxonomical features are the edge of os frontale and foramen infraorbitale structure (Cais 1978).Important additions to the morphological criteria are: the shape and size of formina incisiva and M1 crown's width dimensions as well as maxillary tooth-row length (Ruprecht 1979).

R e s u l t s
As a result of the study, four new pygmy field mouse sites have been confirmed in the vicinity of cities Siecieborzyce, Legnickie Pole and Środa Śląska, as well as on Cisowa Skała.The first three from the described stations are located in the western part of the country, on the plains.Cisowa Skała station is located in the western end of the Pienińskie Pasmo Skałkowe (Fig. 2).1955-1960 ■ 1961 -1970 ■ 1971 -1981 ■ 1982-1992 □ 1993-2004 Fig. 2. Pygmy field mouse stations occurrence in Poland, between 1955 and2004.Stations from Siecieborzyce, Legnickie Pole and Środa Śląska in western Poland are located in a significant distance from hitherto described ones, in the north-western direction.Siecieborzyce are circa 50 km away from the closest previously known stations.
The numberof the mouse derived from pellet material analysis is quite low.In the material from Siecieborzyce a total of 37 bam owl victims have been indicated, from Środa Śląska 5001 long eared owl victims, 416 victims of long eared owl from Legnickie Pole and 237 buzzard victims have been indicated from Cisowa Skała region.In the analysed material, there have been a few pygmy field mouse.In Siecieborzyce, its bone material comprised 2,7% of the material, in Środa Śląska it was 0,2%, and at Cisowa Skała it was 4%.
The rodent does not form a dense population.In Poland, the mouse has been confirmed in 50 UTM squares.The population is spread on an estimated area of 4,800 sq m, which amounts to 1,52% of the counties' total surface.The stations are positioned as islands (Fig. 3).In the majority of the squares, only single sites have been confirmed.Only one square had more than ten confirmations.2).
The oldest site of this species in Poland is located on Wyżyna Małopolska.Between 1955 and 1988 consecutive sites have been confirmed, creating a spread population (Ruprecht 1983, Sałata-Piłacińska & Rachowiak 1990, Lesiński 1991).In the same time the sites of the mouse have been confirmed in the south-werstern part of the country (Nikodem & Ruprecht 1976, Ruprecht 1983, Ziomek 1998).There is a significant probability that this population is joint with a Ukrainian population, which in turn is located in the center of the species' geographical range.
Most stations are located in a highland landscape and in low, warm mountains, such as Pieniny.The rodents' presence has not been confirmed in other mountain ranges, such as Sudety Mountains and Carpathians.A typical lowland region inhabited by pygmy field mouse is located in western Poland.
The dispersion data analysis indicates that geographical range of the species in Poland is wider than expected.The most recent site, confirmed in 2004, is located in the southern part of lubuskie voivodship, outside the previously indicated population's range (Storch 1999).Both the time and spatial dynamics of the rodent's indications are largely a result of researchers' activity.The most sites have been confirmed in the 1970's.After 2000, only five stations have been confirmed.It should be noted, however, that analogous research carried out simultaneously in other parts of the country has not confirmed the presence of the species.
In years 1957-64 Humiński (1964) captured 18 specimens near Wroclaw.Meanwhile in places, where pygmy field mouse is numerous, it is frequently indicated in faunistic coverage.In agricultural environment of Morawy this rodent is one of the prevalent species (Heraldova et al. 2007).Intensification of the research often leads to the confirmation of new sites, as it has happened in Lithuania (Juśkaitis et al. 2001, Juśkaitis 2003).
Exceptions to the country's area range of the rodent are sites located in Pieniny.Haitlinger & Szyszka (1975) captured there 164 specimens.The highest altitude capture locations are 800 m over sea level.This population, along with the stations located in Kotlina Orawsko-Nowotarska is isolated from the rest of the country by forested Beskidy Mountains.The stations from Pieniny might be connected to the Slovakian population.However, expansion of the species from the westernmost Pienińskie Pasmo Skałkowe is unlikely due to moist, marsh biotopes located in the center of Orawa.The station from Cisowa Skała aforementioned in this publication is located in the same UTM square, in which the species was confirmed in the 1970s (Haitlinger & Szyszka 1975).Pieniny Mountains population's large size can probably be attributed to the environmental conditions found there, such as meadows with siccophile vegetation.Contemporary studies carried out in the Slovakian part of Pieniny Mountains, where pygmy field mouse was frequently captured, support that (Cislakova et al. 2004).
A c k n o w l e d g e m e n t s We thank Grzegorz Lesiński, PhD (SGGW Warszawa) for granting us access to specimens' numerosity data from his research.

Fig. 1 .
Fig. 1.Geographical dispersion of pygmy field mouse population, based on Krystufek et al. 2008 and data from own research.
Fig. 3. Number of pygmy field mouse confirmations in UTM squares