The value of a random sampling design for annual monitoring of national populations of larger British terrestrial mammals

Making use of an extensive network of volunteer birdwatchers, this study illustrates how a large-scale monitoring scheme originally designed for common breeding birds can be adapted to also provide robust monitoring data for medium-to large-sized, easily detectable terrestrial mammals. Compared with bird monitoring, the monitoring of common and widespread terrestrial mammals is rarely carried out using a well-designed sampling design and is largely restricted to sites selected by the observer or biased towards particular habitats of interest, making it difficult to know whether trends are representative of the populations of interest. In response to the scarcity of reliable mammal monitoring data in the UK, the principal national bird monitoring scheme, the Breeding Bird Survey (BBS), was expanded to collect information on mammals. The focus was on larger, easily detectable species, although observers have the opportunity to record any mammal species. Here, we present population trends at national and regional scales for nine species of common mammal over the first 18 years of BBS mammal monitoring and examine these in relation to our current knowledge on these species. We further discuss the potential of these data for addressing important questions of conservation and management concern which may be difficult to explore with existing data.