Tracks in snow and population size estimation: the wolf Canis lupus in Finland

The estimation of large carnivore populations presents major logistical challenges. We examined trends in the wolf Canis lupus population in Finland using two independent methods. We compared track indices from an annual wildlife winter census based on a constant, nationwide network of transect lines (wildlife triangles) with the number of reproductions confirmed to occur in the same year during 1996 to 2009. Nationwide, and in the eastern management zone, which is the core area of Finnish wolves, the frequency of wolf tracks in wildlife triangles (% of all triangles counted in a given year having wolf tracks) predicted quite well the log transformed number of reproductions taken place in these areas (adjusted R-2-values for linear regression models 0.59 and 0.68, respectively), while not for the western management zone (R-2 = 0.38). However, although mean wolf densities were low (< 1 wolf/1000 km(2) nationwide and < 3 wolves/1000 km(2) in the eastern zone), track indices could detect the major trends in Finland's wolf population. A clear reason for this was the substantial changes in population size during the study period.