Predicting the future of Capercaillie (Tetrao urogallus) in Finland

Risk analysis is increasingly used in assessing the future of rare and vuln erable species. Often, the probability of the extinction of a population in certain time horizon is assessed. Risk analyses are based on a stochastic model of population dynamics. The assumptions about the population model an d the values of parameters are crucial in risk analysis: small changes in m odel assumptions or parameter values can lead to markedly different results . Thus, the results of risk analysis should be interpreted very carefully. However, even if the results are uncertain, they can provide useful insight for the population dynamics and also reveal the possible gaps in the knowl edge of species ecology. In this paper, the future of capercaillie in diffe rent regions in Finland was assessed with risk analysis. The risk analysis was carried out using Bayesian population dynamics modeling. In the analyse s, Finnish wildlife triangle census data (1989-1997) were utilized and annu al density, breeding success and adult sex ratio were computed for each stu dy region from the data. Because the annual mortality rates cannot be direc tly measured from the wildlife triangle data, the analysis was performed wi th two different assumptions of the mortality rates for adult and juvenile birds: (1) the mortality rates are density dependent; and (2) mortality rat es are not related to density. The results of risk analysis with these two assumptions differed considerably. If the mortality is strictly density dep endent, the future of capercaillie seems secure, whereas in other case the future seems quite difficult. To be able to produce more reliable estimates about the future of capercaillie in Finland more detailed information abou t regional and annual variation in mortality rates as well as the pattern o f density dependence of mortality rates are needed. (C) 2000 Elsevier Scien ce B.V. All rights reserved.