A technique for quantitative estimation of small mammals traversing water obstacles

A new method for quantitative study of small mammals swimming across water obstacles was developed. A line of 25 traps was installed on either poles or boards (“rafts”) with anchors at a distance of 20–25 m from the bank and with 10-m distances between the items. The study was performed upstream along the Ilych River in August 2013. A total of 300 trap/day were accumulated. Twenty-four small mammal individuals of 8 species were captured. Their relative abundance was estimated as the number of individuals per 100 trap/day. It was found experimentally that floating poles neither repel nor attract animals. When an individual accidentally finds a floating pole, it climbs up and explores it for some time. The number of animals per total length of rafts per time unit can be suggested as an index of intensiveness of migration across a water obstacle. In the area studied, the number of small mammals of various species crossing the river was estimated at 26.7 individuals per 1 km/day. A length of 5 m for floating poles/boards and installation of two traps at the ends of an item is suggested to be used.