1067-4136/02/3306- $27.00 © 2002 MAIK “Nauka /Interperiodica” 0434 Russian Journal of Ecology, Vol. 33, No. 6, 2002, pp. 434–439. Translated from Ekologiya, No. 6, 2002, pp. 460–465. Original Russian Text Copyright © 2002 by Saveljev, M. Stubbe, A. Stubbe, Unzhakov, Kononov. Studies on the movements of animals are exception- ally important for understanding their ecology (McCullough, 1985). Although such studies with spe- cies that lead an exclusively hidden life are difficult, substantial information on the migrations of Eurasian (Castor fiber) and Canadian (C. canadensis) beavers has been accumulated to date. However, most studies dealt with postintroduction migrations, i.e., beaver movements after transplantation to new habitats. Thou- sands (Zharkov, 1961; Lavrov, 1980), hundreds (Berg- hofer, 1961), or tens (Hibbard, 1958; Rosell and Nolet, 1997) of tagged beavers were transplanted. Data on migrations over distances longer than 200 miles (Libby, 1957) or 500 km (Lavrov, 1980) are interesting in terms of estimating the physical capacities of animals but cannot be used for characterizing the autecology of the species. Many studies on biotelemetry, including implantable telemetry, have been performed. As a result, the daily activity of beavers and their relation- ships in families have been described in detail (Sokolov et al., 1977; Lancia et al., 1980; Davis et al., 1984; Sukhov, 1986). The results of some other interesting studies were difficult to use, because, e.g., the movement distances were measured directly on a map without regard for meandering of rivers (Leege, 1968), or experiments were interrupted at the most interesting point because of mass deaths of beavers from tularemia, and, when discussing the age-related characteristics of migrations, only the age of beavers at the moment of tagging was indicated (Beer, 1955). In some cases, there were no returns of tagged beavers, repeated catching notwith- standing (Rosell and Nolet, 1997). In addition, living conditions for beavers in the mountain river (in the Sayan Mountains) where we performed our studies considerably differed not only from biotopes located far from them, e.g., on the Elba (Nicht, 1967), but also from almost all biotopes in the vast geographic range of the genus Castor . MATERIALS AND METHODS The region of field studies. The studies were per- formed in the Azas State Nature Reserve located in the Todzhinskii kozhuun (district) of Tyva Republic in Sep- tember 1997 and August 1998, 1999, and 2000. The total area of the reserve is 300390 ha (Molokova and Kartashov, 1999). The basin of the Azas River covers the greater part of the reserve. The river length is more than 150 km. The studies were performed in an approx- imately 100-km section of the Azas in its middle and lower reaches (figure), where absolute elevations at the shoreline varied from 1080 m near the Dom Uchenykh station to 945 m near the river mouth, i.e., near the lower beaver settlement. With a total elevation drop of 135 m, the average slope of the entire study area is 1.3%; along the river section especially rich in rapids, the slope is more than 2%. This white-water section of the river is about 15 km long, with an elevation drop of 35 m (from about 1045 to 1010 m above sea level). It is almost impassable for motor and oared boats and is not populated by beavers. This section of the river divides the Azas beaver population into the upper and lower subpopulations (located upstream and downstream from the white-water section, respectively), which are almost isolated from each other. Natural Movements of Tagged Beavers in Tyva A. P. Saveljev 1 , M. Stubbe 2 , A. Stubbe 2 , V. V. Unzhakov 3 , and S. V. Kononov 4 1 Zhitkov All-Russia Research Institute of Game Management and Fur Farming, Russian Academy of Agricultural Sciences, ul. Engel’sa 79, Kirov, 610000 Russia 2 Zoological Institute, Martin Luther University, Domplatz 4, Halle, D-06099 Germany 3 Azas State Nature Reserve, ul. Zelenaya 14, Toora-Khem, 668530 Tyva Republic, Russia 4 Krasnoyarsk State University, pr. Svobodnyi 79, Krasnoyarsk, 660062 Russia Received May 22, 2001 Abstract—Ninety-three beavers were tagged in 1998–2000 on the Azas River (Tyva Republic), and 28 returns were obtained within one to two years. The results of the study indicated that, unfavorable environment not- withstanding, most beavers did not move outside their settlements. Animals under two years of age were espe- cially active. Females were more resident, whereas males migrated over longer distances. The section of the Azas River with numerous rapids was not an insuperable obstacle for the animals; genetic exchange between the upper and lower subpopulations was found to occur through this section. Key words: migrations, beaver, populations, number of families.