It is generally expected that predators affect the breeding biology of prey species, but most studies have had a prey-biased view of the predator-prey relationship. Without studying the predator, one may draw erroneous conclusions of how predators and prey interact and conservation strategies for prey species could therefore be misleading. In this thesis, I investigated whether omnivorous avian generalists known to depredate nests of passerine birds, mainly the magpie (Pica pica) and the hooded crow (Corvus corone cornix), affected breeding habitat selection and population dynamics of one of their prey species, the red-backed shrike (Lanius collurio) in a Swedish farmland landscape (c. 94 km 2). The studies were performed between 1997 and 2003. My results showed that red-backed shrikes avoided to breed close to magpies and hooded crows, and that the spatial dynamics of red-backed shrikes between years were linked to corresponding spatial dynamics of the two corvid species. By avoiding corvids, red-backed shrikes increased their breeding success. The distribution and population dynamics of magpies were closely linked to human settlements. Thus, in areas with many houses and farms, magpies occurred in higher population densities and had higher repro d ucti ve success than in areas with few houses and farms. The studied magpie population increased in numbers by c. 86% between 1997 and 2003. At the same time did the red-backed shrike population decrease by c. 40% and this decline in numbers was closel y linked to the increase of magpies both at a landscape and at a local scale (km 2 -squares). My results also suggest that corvid nest predators form a search-image for shrub nests and therefore display density-dependent nest predation. However, the density-dependent nest predation risk was nest-site and time specific. Thus, corvids formed a search-image for nests in junipers early in the season, while it was changed towards thorny deciduous shrubs late in the season, probably as a result of corresponding seasonal changes in shrub specific nest densities. My results suggest that the effects of nest predation potentially could affect nest site choice, habitat patch choice and population dynamics of many song birds
