A general approach of using hair-tubes to monitor the European red squirrel: A method applicable at regional and national scales

Monitoring constitutes a key element in the management and conservation of many mammal species. We describe a technique to obtain population indices for red squirrels (Sciurus vulgaris) using hair-tubes and compare these indices to population estimates obtained by live trapping. Data were collected in seven study areas in the Western and Central Alps in Italy and compared with data previously collected in 11 sites in northern England. The aim was to test if hair-tube census could be used to derive a general predictive model allowing accurate predictions of squirrel numbers in different years, habitats and geographic regions. We used model equations developed from the proportion of hair-tubes visited to predict densities obtained from live-trapping. Hair-tube data gathered in the Central Alps correctly predicted squirrel densities in the Western Alps. A combined data set pooling the sites of these two regions based on the first three years successfully predicted the two successive years. In addition, a combined model derived from areas monitored for five years had a high predictive value locally (89%) and internationally (73%) when applied to the English data set. We therefore believe that the predictive model developed in this study could be of general value and be used to monitor squirrel populations in European low density conifer habitats (0.1–0.5 squirrels/ha). The approach may also be suitable for many tree squirrel populations in North America and other arboreal rodents that occur at similar densities.