Predation on artificial nests in relation to the numbers of small mammals in the Krusne hory Mts, the Czech Republic

The alternative prey hypothesis suggests that generalist predators switch from their primary prey to secondary when the former is scarce. We tested this hypothesis during a two-year study combining data on predation of ground dummy nests and the numbers of small mammal populations in a highly fragmented landscape in the Krusne hory Mts, the Czech Republic. A significant decrease of small mammal numbers between 2002 and 2003 was followed by a considerable increase of predation on artificial nests from 34% to 76%. Most of the nests (64.7% of the documented cases in 2002) were predated by medium-sized mammals such as marten and fox, common in our study area. Only 8.8% were predated by avian predators (corvids) occurring infrequently in our study area. The results support the alternative prey hypothesis and suggest that in the Krusne hory Mts the nesting success of ground nesting birds may Vary strongly from year to year depending on the cycle phase of small mammals, the main prey of dominant predators.