Evaluation of sign surveys as a way to estimate the relative abundance of American mink (Mustela vison)

American mink Mustela vison are an invasive species in many parts of the world (e.g. Europe, Iceland and South America) and in many of these areas they are a threat to the native wildlife. It is therefore important to establish a reliable and efficient method to estimate their relative abundance in order to manage their populations. In this study, the use of surveys of signs (scats and footprints) as a way to estimate the relative abundance of American mink was evaluated. Populations of mink in three areas of England were studied to evaluate the impact of three factors (surveyor, marking places and month) on the probability of deposition and detection of signs. Among these factors only month had a significant effect. In the second part of the study, sign surveys were compared with live trapping and it was found that the proportion of sections with mink signs was only loosely correlated to the abundance of mink as estimated from live trapping. In conclusion, this study suggests that, provided that surveyors are trained, that there is a sufficient number of marking places in each section, and that the surveys are carried out in comparable seasons, sign surveys are an appropriate way to monitor the relative abundance of mink. Sign surveys are better than trapping when it is necessary to monitor mink populations over large areas because they are less time consuming, require less manpower and are cheaper.