The recent development of Oistance Sampling techniques (OS) has provided a promising device to yield good population estimates with samples of small size (40-80 independent detections) with reasonable survey costs. On this subject, during the past Roe deer Meeting (Portugal) were presented interesting results suggesting that OS coupled with thermal imaging (IR) could be a suitable and costeffective monitoring methodology. We present the results of a 3-year project devoted to compare density estimates from OS & IR with more conventional Mark Recapture (MR) estimates of an Appennines roe deer population. We worked in an open hunting estate, where a long-term study on roe deer ecology includes radio-monitoring and densities assessment since 1995. We tested the possibility to survey roe deer using a portable thermo-camera, equipped with a laser rangefinder and an electronic compass, which allows the operator to record ani mais presence (group size and number of groups) also in completely dark night and to measure their distance and angle with respect to the observer. We walked 35 transects (total effort 20.5 km) in 3 nights, from 7:00 PM to 5:00 AM, to survey an area of 523 ha. We made 2 survey replicates each year (late winter/early spring) to compare the results with estimates of early spring survey calculated by MR methods. Night survey is thought to mitigate the problem of g(O) < 1 (which affect daylight ones when animals f1y away reacting to the presence of an observer) because the use of an IR camera is supposed to allow the detection of deer before being discovered. However, IR & OS survey design could be biased because observers are forced to use paths and so transect positioning may not be random with respect to ani mais distribution. We present an a posteriori evaluation of the survey design and we compare the 2 survey methods in order to assess the presence of biases in IR & OS.
Distance Sampling and Thermal Immaging to assess a roe deer population in Northern Appennines: the pros and cons of a fashionable technique / Franzetti, B; RAGANELLA PELLICCIONI, E; Focrdi, S; DE MARINIS, Am; Marini, Francesca; Busatta, S. TOSO S.. - (2005), pp. 41-41. (Intervento presentato al convegno VII European roe deer meeting tenutosi a Jerez de la Frontera-Càdiz, Spagna nel 10-12 Marzo 2005).