Proceedings of the 8 th International Scientific Conference Rural Development 2017 Edited by prof. Asta Raupelienė ISSN 1822-3230 / eISSN 2345-0916 eISBN 978-609-449-128-3 Article DOI: http://doi.org/10.15544/RD.2017.171 Copyright © 2017 The Authors. Published by Aleksandras Stulginskis University. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC-BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. EURASIAN BEAVER (CASTOR FIBER L.) POPULATION IN ASU SCIENCE AND TEACHING HUNTING AREA AND BEAVER DAMS REBUILD INTENSITY Monika RAŠKAUSKAITĖ, Institute of Forest biology and Silviculture, Faculty of Aleksandras Stulginskis University, Address: Studentų g. 9, Akademija Kaunas dist., Lithuania; monika.raskauskaite@asu.lt (corresponding author) Kastytis ŠIMKEVIČIUS, Institute of Forest biology and Silviculture, Faculty of Aleksandras Stulginskis University, Address: Studentų g. 9, Akademija Kaunas dist., Lithuania; kastytis.simkevicius@asu.lt Eurasian Beaver (Castor fiber L.) was reintroduced in Lithuania on 1947. Population growth was quite rapid ant there were about 6000 beavers on 1970. Nowadays beavers population in Lithuania is about 40 000. Beavers have a possibility to affect the environment where they live by building dams, lodges, making burrows systems, changing water level. Because of being such an active environmental former beaver has a huge indirect impact for forest and agricultural fields – higher water level usually causes damage for forest trees or crops. There are different studies about this beaver’s ability to change environment and to build dams, lodges. Explanations why it is needed for this species now is clear, but still there are question how can these animal plan, organize and improve their ability to build. The aim of this research is to find out if dams rebuilt activity intensity differs during different year seasons and is it affected by the beaver’s family size in current place. According to our findings, the beginning of dam rebuilt and total d am rebuild depends on year season – on fall season it takes 4 times less time. In addition to this, family size has an effect – bigger families rebuilt dams faster. Usually beavers do this job from midnight to 2 a.m. on fall season. Keywords: Eurasian beaver, dam, rebuild, population INTRODUCTION Due to over-hunting Eurasian Beaver survived in eight relict populations in Europe and Asia (Nolet and Rosell, 1998). Until the XIX century the European Beaver was widespread in Lithuania but due to the high value of fur population of beaver rapidly decreased. In the beginning of 20th century there were no beavers permanently living in Lithuania (Prūsaitė, 1988). Eurasian beavers have, since the late 19 th century, staged a remarkable recovery both in population and distribution (Halley et al., 2012). In Lithuania this species was reintroduced on 1947 by professor Tadas Ivanauskas. They were carried in from the Voronezh Reserve later on from the Gomel region. Also, after the Second World War beaver began to spread naturally from Belarus to Lithuania. Nowadays the European beaver is a widespread rodent in Lithuania. According to the official statistics, there were 40.6 thousand beaver in Lithuania on 2017 (Lietuvos Respublikos..., 2017). According to other researchers, beaver in Lithuania is even more numerous. The average estimate density of the beaver sites in Lithuania is 4.12 / 1000 ha. Minimal estimated beaver site number in Lithuania is 22000 - 31000 (Ulevicius, 2008). A local beaver population investigated in hilly laky moraine uplands, reaching high density 19 beaver site / 1000 ha (Bluzma, 2003). Density of the beaver population was not even through the country. North-western, north-eastern and south-eastern parts of Lithuania were characterized by the highest density of beaver sites. Relatively low density of beaver sites was characteristic for some districts of northern, eastern and middle parts of Lithuania (Ulevicius, 2008). Now it is known that the beavers are an important factor in the development of ecosystems, and there is one of the most important animals in renaturalizing the anthropogenic environment (Данилов, 2007). Beaver activities that impacts ecosystems can be grouped into two main groups. The first group includes the use and preparation of nutrients when trees and shrubs of varying sizes are cutting down. In this way beaver not only produce food but also creates a lot of dead wood that is not numerous in today's intensively managed forests (Andersson et. al, 2005). The second group of activities includes the constructions of beavers. The construction activity is divided into two subgroups: (1) construction of shelters (burrows systems, lodges) and (2) other structures for improving the living environment (dams and channels). Beaver activity can also have a direct and indirect impact on other components of biocenosis (Данилов, 2007). Beavers have a unique ability to modify their environment by actively building dams. Dams are built to maintain a high and constant water level. Such a level of water is necessary for the safe and rapid movement of animals, for a food