1352 PUBLIC AND SCIENTIFIC BEAR LITTER SIZE Life history and population demography charac- teristics are important information for wildlife man- agers because they are needed for managing hunt- ing or conservation efforts. Although Knight and Eberhardt (1985) have pointed out that adult female survival is the most important variable influ- encing population growth in brown bears (Ursus arctos), litter size is an essential parameter when calculating reproduction for population models for bears (Wiegand et al. 1997, Sæther et al. 1998, Freedman et al. 2003). Obtaining accurate mean values of litter sizes for bears is an expensive and difficult task because it usually requires counting the offspring of radiocollared females for several years due to variations in litter size within and among females. Female American black bears (U. americanus) may be visited in their maternal dens to determine the number of offspring (McDonald and Fuller 2001, Noyce et al. 2002); however, for human safety reasons it is not advisable to visit maternal brown bear dens. Spring litter size in brown bears is mostly obtained by direct observa- tion after the family has left the den (Craighead et al. 1995). If no female bears are radiocollared, infor- mation on litter sizes often is obtained from report- ed observations by the public. The management of several brown bear populations, some of them small and endangered, relies on litter sizes obtained by observations by the public (Austria—Rauer et al. 2001; Finland—Kojola and Laitala 2000, Slovakia— Hell and Slamecka 1999; Spain—Naves and Palomero 1993,Wiegand et al. 1997) as well as the acquisition of basic biological information of poorly known bear species (e.g., Andean bear [Tremarctos ornatus]—X. Velez-Liendo, Laboratory of Animal Ecology, Univ. of Antwerp, Belgium, personal com- munication). Observations of females with cubs also are important in the monitoring of the brown Wildlife Society Bulletin 2005, 33(4):1352–1356 Peer refereed Address for Andreas Zedrosser: Institute of Wildlife Biology and Game Management, Department for Integrative Biology, Univer- sity of Natural Resources and Applied Life Sciences, Vienna, Peter Jordan Strasse 76, A - 1190 Vienna, Austria, and Department for Ecology and Natural Resource Management, Norwegian University of Life Sciences, PO Box 5003, NO - 1432 Ås, Norway; e-mail: andreas.zedrosser@umb.no. Address for Jon. E. Swenson: Department for Ecology and Natural Resource Management, Norwegian University of Life Sciences, PO Box 5003, NO - 1432 Ås, Norway, and Norwegian Institute for Nature Management, Tungasletta 2, NO - 7485 Trondheim, Norway. Do brown bear litter sizes reported by the public reflect litter sizes obtained by scientific methods? Andreas Zedrosser and Jon E. Swenson Abstract Litter size, an important reproductive parameter used in the management and conserva- tion of brown bears (Ursus arctos), is determined from reported observations by the pub- lic in some areas. We compared brown bear litter sizes based on reported public obser- vations with those obtained by counting young from a helicopter or the ground by researchers. Mean litter sizes based on public observations were lower and showed more variance between seasons (spring and autumn) than mean litter sizes based on research methods. Public mean litter sizes showed significant variation among years, unless data from at least 6 years were analyzed. In south-central Sweden annual correction factors ranging from 1.120–1.260 must be used to correct the mean litter size based on public observations to agree with the mean litter size obtained by research, depending on how evenly public observations are spread throughout the year. Key words brown bear, litter size, Ursus arctos