Laima Balčiauskienė

The Diet of rhe Tawny Owl (Strix Aluco) in South-Western Lithuania during the Breeding Period

The paper presents the material on the Tawny Owl (Strix aluco) diet collected during the breeding period (April–May) in Sakiai district. Prey remains from 11 nestboxes occupied by owls in 1986–1987 and 1997–2004 were analysed. The remains of 15 small mammal species, 18 bird species, two amphibian species and two genera of insects were recovered. The dominating small mammal species (n = 361) were Clethrionomys glareolus (24.6%), Microtus arvalis (20.5%), Apodemus flavicollis (11.6%), Microtus agrestis (8.8%) and Sorex araneus (8.6%). Among birds, the most often preyed were Turdus philomelos, T. merula, Fringilla coelebs and Coccothraustes coccothraustes. Frogs Rana arvalis and R. temporaria as well as insects Dytiscus sp. and Melolontha sp. were also present in the food remains. The species composition and the number of small mammals preyed in Sakiai district were compared to the respective data from Kėdainiai district, Kurtuvėnai Regional Park and Kamanos Strict Nature Reserve. The diet of the Tawny Owl i...

Analysis of Tawny Owl (Strix Aluco) Food Remains as a Tool for Long-Term Monitoring of Small Mammals

Data on the Tawny Owl diet from the prey remains found in nestboxes after a breeding period in 1997–2004 in Kėdainiai district and in 1999–2003 in the Kamanos State Strict Nature Reserve are compared with the results of small mammal monitoring in these territories. The number of small mammal species found in the owl prey remains as well as their diversity was always greater, than that obtained by trapping. On average, 12.1 ± 0.9 species were recovered from prey remains in Kėdainiai, 11.3 ± 1.9. in Kamanos State Strict Nature Reserve, while the number of species trapped was 7.0 ± 0.6 and 6.8 ± 1.7 accordingly. Shannon.s H in prey remains was 2.62 ± 0.11 and 2.80 ± 0.14 vs. 1.97 ± 0.13 and 1.65 ± 0.33. It is obvious, that quite a lot of small mammals that are seldom trapped are found in owl prey. Analysis of prey remains may be used as a method for small mammal monitoring.

Diet of Tawny Owl (Strix aluco) and Long-Eared Owl (Asio otus) in Lithuania as Found from Pellets

Diet composition and food niches of two common and widespread in Lithuania owl species, Tawny Owl (Strix aluco) and Long-eared Owl (Asio otus), were analysed from irregularly collected pellets. S. aluco was characterised by a more diverse diet and a wider food niche: 14 small mammal (93.1% of the recovered items) and two amphibian (5.2%) species, a few passerine birds (1.1%) and representatives of three Coleoptera groups (0.6%) were recovered, whereas for A. otus – nine small mammal and two Carabidea species. By numbers, primary food resources of S. aluco were C. glareolus (31.4%), M. arvalis (27.9%) and A. flavicollis (14.3%), whereas of A. otus - M. arvalis (70.8%), all Microtus voles constituting 95.2%. Diet diversity of S. aluco was more than twofold higher (Shannon’s H = 2.62 vs. 1.16). According to biomass, main foods consumed by S. aluco were C. glareolus, M. arvalis and A. flavicollis (27.6, 25.0 and 22.4%, respectively). For A. otus, Microtus voles represented 95.8% of biomass consumed (M. arvali...

Identification of Shrews and Rodents from Skull Remains according to the Length of a Tooth Row

In the article, measurements of lengths of maxillary and mandibular tooth rows in three species of shrews (Sorex araneus, S. minutus, Neomys fodiens) found in Lithuania, the birch mouse (Sicista betulina), six species of mice (Mus musculus, Apodemus agrarius, A. flavicollis, A. sylvaticus, A. uralensis, Micromys minutus), and three species of voles (Microtus arvalis, M. oeconomus, M. agrestis) are presented and suitability of these measurements for species identification given. It has been established that according to these measurements species of shrews can be identified unmistakably. Species of mice and voles could be identified with reservation. Intervals are presented within the ranges of which species of mice and voles could be identified. The method is useful while working with incomplete skulls, such as those found in owl and birds of prey pellets. While using data from mammal identification keys and from other literature sources of foreign countries for identification of mammals of Lithuania, pos...

Coincidence of Small Mammal Trapping Data with their Share in the Tawny Owl Diet

Data for 1997–2005 on the Tawny Owl (Strix aluco) diet during the breeding period (food remains from nest-boxes after breeding) were compared with long-term (spring and autumn 1997–2004) data on small mammal monitoring and short-term trapping data obtained close to owl nest-boxes (autumn 1999 and 2000). The investigated sites were located in the Kėdainiai district (central Lithuania). A total of 18 mammal species were identified in the diet (91.3% of 2,042 identified remains). In general, mammal diversity in the diet was much higher (9 to 15 species recovered annually) than in trapping. Owls mainly preyed on bank voles (31.0% of all recovered mammals), short-tailed voles (15.8%, Microtus in total – 29.5%) and yellow-necked mice (14.6%). At the monitoring site, 969 individuals of 12 species (5 to 10 species annually) were trapped. Dominant was the bank vole (47.6%), followed by the yellow-necked mouse (18.7%) and common vole (14.1%, Microtus in total – 16.4%). A total of 193 individuals of 9 small mammal s...

Root vole, Microtus oeconomus, in Lithuania: changes in the distribution range.

Abstract. Lithuania is on the edge of the main distribution range of the root vole (Microtus oeconomus). It was found that the trappability of M. oeconomus did not depend on the trapping effort, the number of recorded species and individuals or the species diversity. All 13 localities with proportions of M. oeconomus constituting over 30% of the small mammal community are situated in the south and west of Lithuania. Analysis of data collected over 50 years confirms that the species has become more abundant, more widespread and its distribution range has spread north and east from the south and west of the country. The main habitats for M. oeconomus in Lithuania are reedbeds, meadows, shrubby areas and shores of water bodies. Abandoned former agricultural areas create suitable habitats for the species, thus promoting its increased abundance and wider distribution.

CRANIAL GROWTH OF CAPTIVE BRED BANK VOLES (CLETHRIONOMYS GLAREOLUS)

The cranial growth of C. glareolus was investigated using 444 captive bred individuals, aged from 5 to 680 days. Three growth patterns of skull characters were found: (1) rapid growth in the first decade of age, followed by a very slow change or stabilisation (width of molar M1 and length of maxillary tooth row), (2) long period of flat growth (length of mandibular tooth row and length of mandibular diastema), and (3) long period of initial growth followed by the plateau phase (length of nasalia and length of foramen incisivum). The measurements of skull characters correlated best with body weight, whereas correlations with body length or individual age were less expressed. Out of 20 skull characters tested, the strongest correlation with animal age and body weight was observed in the length of cranial (upper) diastema. Other characters, which correlated with animal age, were the length of nasalia and the length of molar M1. In captive bred individuals, fluctuations of body weight and skull measurements w...

Preliminary Assessment of Damage Caused by the Wolf in Lithuania

According to the data of a questionnaire research carried out in 1999–2001, a preliminary assessment of damage caused by wolves in Lithuania is given. The most serious damage was recorded in Biržai, Kelmė, Joniskis, and Siauliai districts. Depredation cases were most common in summer and autumn. Cattle, sheep, and dogs were attacked not only in pastures, but also in farmsteads and even villages, even if dogs were kept in yards. One fourth of the attacks was recorded further than 1 km from forests. As a rule, animals were not guarded in the day time and were left in pastures for the night. Usually they were uninsured, so losses were not compensated. According to livestock owners who had suffered losses, the damage should be compensated by the Ministry of Environment or the Ministry of Agriculture and hunters. According to a preliminary assessment, at present wolves annually kill about 400–1,200 animals in Lithuania; this is fewer than in the 1920s or mid-1950s, but more than in neighbouring Latvia. Owners ...

The impact of Great Cormorants on biogenic pollution of land ecosystems: Stable isotope signatures in small mammals.

Studying the isotopic composition of the hair of two rodent species trapped in the territories of Great Cormorant colonies, we aimed to show that Great Cormorants transfer biogens from aquatic ecosystems to terrestrial ecosystems, and that these substances reach small mammals through the trophic cascade, thus influencing the nutrient balance in the terrestrial ecosystem. Analysis of δ(13)C and δ(15)N was performed on two dominant species of small mammals, Apodemus flavicollis and Myodes glareolus, inhabiting the territories of the colonies. For both species, the values of δ(13)C and δ(15)N were higher in the animals trapped in the territories of the colonies than those in control territories. In the hair of A. flavicollis and M. glareolus, the highest values of δ(15)N (16.31±3.01‰ and 17.86±2.76‰, respectively) were determined in those animals trapped in the biggest Great Cormorant colony. δ(15)N values were age dependent, highest in adult A. flavicollis and M. glareolus and lowest in juvenile animals. For δ(13)C values, age-dependent differences were not registered. δ(15)N values in both small mammal species from the biggest Great Cormorant colony show direct dependence on the intensity of influence. Biogenic pollution is at its strongest in the territories of the colonies with nests, significantly diminishing in the ecotones of the colonies and further in the control zones, where the influence of birds is negligible. Thus, Great Cormorant colonies alter ecosystem functioning by enrichment with biogens, with stable isotope values in small mammals significantly higher in the affected territories.

The influence of spring floods on small mammal communities in the Nemunas River Delta, Lithuania

The influence of the annual spring floods on small mammal communities was studied in the Nemunas River Delta, SW Lithuania. The aim of the investigation was to compare the diversity of small mammals inhabiting spring-flooded meadows, meadows not subjected to flooding and spring-flooded forest in years characterized by differing heights and durations of spring flood. In the years of the high flood, the number of species and diversity index were higher, while index of dominance was less than in the years of low flood. Significantly, the highest proportions of Apodemus agrarius were recorded in spring-flooded meadows in years of high flood (41.7%), while Microtus oeconomus occurred in the highest proportions in spring-flooded meadows in years of low flood (66.8%) and in meadows not subjected to flooding (47.1%). In non-flooded areas, M. Oeconomus is not expelled by the floods and outcompetes other species. After high levels of flooding, during the process of re-population, the voles may be outcompeted by A. agrarius. In the absence of dominant species, greater opportunities existed for the establishment of more species (13 species in flooded meadows). Micromys minutus accounted for up to 19.5–30.1% in the years of high flood. We concluded that the annual spring floods in the Nemunas Delta had no long-term negative effects, the number of small mammal species and their abundance had been restored in just a few months. The worst consequences of the high flood were recorded in forest habitat. Spring floods, and especially the higher floods, are natural environmental agents, maintaining the high diversity of small mammals in meadows and reed-beds.