Multiple habitat associations: the role of offsite habitat in determining onsite avian density and species richness

Many animal populations continue to decline despite occurring in protected areas or on sympathetically managed sites. Frequently, this is because a specifi c habitat patch may not fulfi l all the niche requirements of a threatened species. For instance, species often move between, and make use of, multiple habitat types for breeding, roosting and feeding within the same landscape. Th ese cross-habitat interactions present a challenge for conservation. Here we quantify how the habitat associations of individual species and assemblages occurring within two distinct but adjacent habitat types (moorland and farmland) determine a suite of density and richness indicators, using the bird community of the English uplands as a case study. Th ere was a clear association between onsite avian density and richness and off site habitat structure (e.g. vegetation height, percent cover of dominant plant species, land management practices). Although such eff ects are not universal across all species and assemblages, where present (for fi ve farmland and three moorland indicators) the increase in explanatory power off ered by including off site habitat structure can be large. By constructing scenarios of possible changes to management practice on both moorland and farmland, we demonstrate a real conservation benefi t can be obtained by altering management in off site habitats. For example, reducing burning intensity on moorland can result in a fi ve-fold increase in snipe Gallinago gallinago density on farmland, without an alteration in farmland habitat. For one species (Eurasian curlew Numenius arquata ), we demonstrate the frequency with which birds move between and utilise farmland and moorland during the breeding season, and therefore the importance of both habitat types to maintaining population densities. Th e multiple habitat dependency phenomenon quantifi ed here is common and not restricted to birds. Th e successful conservation of many threatened species will thus depend on coordinated cross-habitat management.