Pitfalls in using counts of roaring stags to index red deer (Cervus elaphus) population size
Paolo Ciucci A B , Gianluca Catullo A and Luigi Boitani AA Dipartimento di Biologia Animale e dell’Uomo, Università ‘La Sapienza’ di Roma, Viale dell’Università 32 – 00185, Roma, Italy.
B Corresponding author. Email: paolo.ciucci@uniroma1.it
Wildlife Research 36(2) 126-133 https://doi.org/10.1071/WR07121
Submitted: 27 August 2007 Accepted: 6 November 2008 Published: 20 February 2009
Abstract
Counting roaring stags during the rut has been proposed as a means to assess deer population size and trends but few, if any, attempts have been made to evaluate the reliability of this technique. By means of a commonly used field protocol, we assessed to what extent relative abundance estimates of red deer (Cervus elaphus) based on roaring-stag counts in the northern Apennines (Italy) were susceptible to exogenous and unpredictable sources of variability. By using up to 26 simultaneous observers in an area of 5218 ha, we estimated densities from 0.45 to 0.61 roaring stags per 100 ha in 3 consecutive years (1992–94), corresponding to annual changes in the number of counted roaring stags ranging from –21% to +35.7%. However, only in two of the three years were seasonal trends and peaks in roaring activity apparent, and timing of the survey was not always synchronous with the roaring peak. In addition, annual and nocturnal variation in roaring activity, and weather conditions during the survey, might have influenced the counts to some extent, probably determining high Type I and Type II error rates. We contend that additional sources of error, associated with unknown demographic and ecological settings, may further increase unreliability of the technique when it is used to estimate absolute density of red deer populations. We conclude by emphasising that managers should not use this method for population monitoring unless they can prove it can yield reliable results.
Acknowledgements
We acknowledge L. Artoni, R. Falasconi, I. Guj, C. Lissoni, L. Manghi, M. Masi, E. Raganella Pelliccioni, S. Ricci, M. Rocco, A. Rossi, P. Trapanese and L. Ventura for their assistance during field work. The Forestry Service of Orecchiella Natural Park, the members of ‘Garfagnana Vacanze’ co-operative, and our friends of Corfino (Lucca, Italy) participated in the peak counts. Funding and logistic assistance were provided by Toscana Region, the ex-A.S.F.D. Administration of Lucca and the Istituto di Ecologia Applicata of Rome. We thank three anonymous referees who provided useful insights and comments on an earlier draft of this paper.
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