FEAR IN FARMLANDS - HOW MUCH DOES PREDATOR AVOIDANCE AFFECT BIRD COMMUNITY STRUCTURE

The abundances of potential avian prey species may be lower in the vic inity of the nests of predatory birds than farther away. We predicted that, if this density depression is due to predation, the observed den sity pattern should develop gradually during the breeding season as ra ptors deplete the prey populations. In contrast, if the low abundance is a result of predator avoidance during breeding habitat selection, t he observed pattern should be evident from the beginning of the breedi ng season. We tested these predictions by counting breeding birds alon g transect lines (length 700 m, width 100 m) radiating away from Kestr el Falco tinnunculus nests, and along control transect lines situated >1000 m from Kestrel nests, five times in the course of the 1994 breed ing season in western Finland. Breeding bird density was ca. 25% lower within 700 m of the Kestrel nests than on control sites. The positive relationship between bird densities and the distance from Kestrel nes ts was most evident in the early breeding season, which supports the p redator avoidance hypothesis. The effect of predator presence on the d istribution of breeding pairs seemed to be weak at species level but s tronger at community level. At the beginning of the breeding season, d istance from predator nests explained a larger proportion of the obser ved variation in the number of birds or species than any of the habita t variables used.