Clevenger, P.A. & Purroy, F.J. 1996: Sign surveys for estimating trend of a remnant brown bear Ursus arctos population in northern Spain. - Wildl. Biol. 2: 275-281.
Brown bears Ursus arctos in Spain's Cantabrian Mountains are continuing to decline in numbers despite their protected status. Recovery plans for this population stress the need for monitoring of occupied habitat using non-intrusive methods. A population monitoring program to estimate bear abundance indices by quantifying tracks and scats (sign surveys) along a network of survey routes was designed. Each route was divided into consecutive 1.6-km segments, which comprised the basic sampling unit, and were assumed to provide independent observations. During a 3-year pilot study surveys were run twice per year, totaling 70 routes, including 950 segments, and covering over 1,500 km annually. Averages of 0.06 sign per segment were observed; only 4% of the segments had sign. It is concluded that the present sampling scheme does not provide enough statistical power to accurately detect significant declines in population level. The difficulties of monitoring trends of low density populations using surveys are recognized. However, by increasing the sampling intensity, more reliable information and greater precision of the population trend estimate should be obtainable. Thus, a future monitoring strategy should be based on increasing sampling intensity and closely monitoring bear distribution and occurrence.
Key words: brown bear, monitoring, population trend, sign survey, Spain, statistical power, Ursus arctos
Anthony P. Clevenger*, Department of Forestry, Wildlife & Fisheries, University of Tennessee, Knoxville, Tennessee 37901 USA and Departamento de Biología Animal, Universidad de León, E-24071 León, Spain
Francisco J. Purroy, Departamento de Biología Animal, Universidad de León, E-24071 León, Spain
*Present address: Wildlife Section, Banff National Park, Box 900, Banff, Alberta T0L 0C0, Canada
Received 16 January 1996, accepted 16 September 1996
Associate Editor: Jon E. Swenson