Populations of most large mammals can be assessed by searching preferred habitats for particular signs such as footprints, dung, burrows or other homes and feeding signs. Riparian animals such as otter and water vole can be assessed by attention to the river-bank habitat, deer by tracks, dung and signs of browsing.
Bats have different roosting habitats in winter and summer with sometimes large numbers gathering during the warmer months in maternity roosts to breed and raise young. The best time to survey for bats is during the late spring and summer, May to July. Surveys are done at dusk using bat detectors and knowledge of bat behaviour and habitats.
Small mammal populations can be assessed by using traps such as Longworth traps to capture individuals which can then be safely released.