Evaluation of four methods used to estimate population density of moose Alces alces Lars Ro¨ nnega˚ rd, Ha˚ kan Sand, Henrik Andre´n,Johan Ma˚ nsson &A ˚ ke Pehrson Ro¨ nnega˚ rd, L., Sand, H., Andre´n, H., Ma˚ nsson, J. & Pehrson, A ˚ . 2008: Evaluation of four methods used to estimate population density of moose Alces alces. - Wildl. Biol. 14: 358-371. Various survey methods are used to monitor and manage ungulate popu- lations. The choice of optimal method depends on estimation accuracy, management objective and financial constraints. Here we compare esti- mates produced by four different methods for estimating population size, i.e. aerial counts, hunter observations, pellet group counts and co- hort analysis. A Swedish moose Alces alces population was studied during 1973-2005 in the Grimso¨ Wildlife Research Area (135km 2 ). The highest correlation was found between cohort analysis and aerial counts (r=0.69, P<0.05), and the hunter observations and the aerial counts (r=0.76, P<0.10). The different methods produced relatively consistent trends in population estimates over years. Pellet group counts prior to 1997 were not significantly correlated with the other methods, probably due to unrepresentative spatial sampling. A comparison of the aerial and pellet group counts in 2002 and 2006, showed that the average defecation rate was estimated at approximately 14 pellet groups per day per moose. Our results show the importance of having representative spatial sampling in pellet group surveys and indicate that hunter ob- servations can be a useful tool for estimating long-term population trends even in moderately sized areas. Key words: aerial count, cohort analysis, deer, hunter observations, manage- ment, monitoring, pellet group counts Lars Ro ¨nnega ˚rd, Linnaeus Centre for Bioinformatics, Uppsala University, BMC, Box 598, SE-75124, Uppsala, Sweden, and Department of Economics and Social Sciences, Dalarna University, Sweden - e-mail: lrn@du.se Ha ˚kan Sand, Henrik Andre ´n, Johan Ma ˚nsson & A ˚ ke Pehrson, Grimso ¨ Wildlife Research Station, Department of Conservation Biology, Swedish University of Agricultural Sciences, SE-730 91 Riddarhyttan, Sweden - e-mail addresses: Hakan.Sand@ekol.slu.se (Ha ˚kan Sand); henrik.andren @nvb.slu.se (Henrik Andre ´n); Johan.Mansson@ekol.slu.se (Johan Ma ˚ns- son); Ake.Pehrson@ekol.slu.se (A ˚ ke Pehrson) Corresponding author: Lars Ro ¨nnega ˚rd Received 14 May 2007, accepted 27 November 2007 Associate Editor: Mads C. Forchhammer An effective system for monitoring wildlife popu- lations enables management and decision-making by providing reliable data on the number of animals, distribution, individual growth rate, reproduction and sex/age composition. Over the years several different survey methods have been used to monitor 358 Ó WILDLIFE BIOLOGY  14:3 (2008)