Kilometric index as biological indicator for monitoring forest roe deer populations

Abstract

During a long term study (10 years) of an increasing forest roe deer Capreolus capreolus (Linnaeus, 1758) population, the reliability of a kilometric index for monitoring population size was tested. Kilometric index was defined by the ratio "number of observed animals/number of kilometers" of standardized transect. Three indexes were constructed: one for each transect, one for a transect set and one for all transects performed during a year. Actual population size was estimated each year by capture - mark - recapture. A modification of Petersen - Lincoln Index allowing long-term use was applied as the reference method. The relationship between annual kilometric index and population size estimation was assessed by calibrating index using linear and logistic regression. Moreover, we looked for different population levels using analyses of variance applied on the different indexes. Although high correlation was obtained between annual kilometric index and reference method, calibration equation led to unreliable population schedule. This demonstrated differential sensitivity of kilometric index according to population levels. Three population levels were discriminated by analyses of variance: a low population level during the four first years, a transition level corresponding to the fifth year and a high population level during the five last years. Indexes defined on a transect set (called "photo") appeared as the more informative. Such a study showed that to look for differential population levels from abundance indexes (bioindicator conception) is more pertinent than to establish conversion equations (calibration conception) in order to monitor forest roe deer population.