Estimation of chamois abundance in the Swiss National Park
Project Number: CH-4451
chamois, focal counts, capture-mark-resight, population abundance
The estimation of wildlife population abundance is a complex and important issue, the key stone for a proper wildlife management. So far it has been assumed that chamois population can be easily surveyed by means of focal counts from vantage points, since this species can be often observed in open areas. However, the recent increase in chamois density and the subsequent colonization of forested areas have raised some concerns about the reliability of focal counts, which could lead to severe bias in the estimate of population size. In my thesis I investigated the size of a chamois population living in the Swiss National Park through the use of focal counts and capture-mark-resight (CMR). Between 1997 and 2008, focal counts have been carried four times per year (January, April, August, November) from vantage point by the experienced personnel of the Park; during the same time span, 125 chamois (44 males, 81 females) have been captured and individually marked with ear tags and/or collars, and their resightings occurred ever since. I compared the outcome of focal counts with the estimates obtained with CMR models, built with three different software (MARK, NOREMARK and CAPTURE). Despite CMR models are traditionally (and successfully) used for estimating abundance, in this research all three software gave erroneous results. Specifically, MARK and NOREMARK overestimated population size, with no significant difference between them, while CAPTURE showed a remarkable underestimation. Such a strong bias is likely due to the insufficient accuracy as far as the fulfilment of some basic CMR assumptions is concerned. The assumption of closed population might have been violated during the survey sessions, while non-consistent survey strategy and low proportion of marked individuals might have directly biased the final estimates of population abundance. Nevertheless, defined minimum number of resightings, distribution of vantage points, usage of a proper marking method, fulfillment of all CMR assumptions, right choose of software and estimator for data set analysis are obligatory for the proper CMR study. The capture heterogeneity is another important issue, which should be taken in consideration, especially during the marking of individuals. Moreover, the use of Minimum Number Alive (MNA) to estimate “marks at risk” should be avoided.
Lavadinovic, V. 2010: Estimation of chamois abundance in the Swiss National Park. Master Thesis. Universität für Bodenkultur Wien.
Last update: 3/20/18
Source of data: ProClim- Research InfoSystem (1993-2020)
Update the data of project: CH-4451