Breeding Success of Pied Flycatchers in Artificial Forest Edges: The Effect of a Suboptimally Shaped Foraging Area

Abstract

We conducted an experimental study of nest-site selection and breeding suc- cess of Pied Flycatchers (Ficedula hypoleuca) in artificial forest edges. The nest-site selection experiment revealed a clear pattern in the order of occupancy of nest boxes by males: boxes situated at the edge between the forest stand and the clearcut were consistently avoided by the earliest-arriving males, which preferentially selected boxes 50 to 100 m from the edge. We also wanted to assess the possible fitness consequences associated with the observed nest location by moving randomly selected breeding pairs to a new location with respect to dis- tance from the edge. The body mass of offspring was lower in nests moved to the edge than in nests moved into the interior of the forest stand. Body mass may be correlated with the lower feeding rate observed at edge nests compared with interior nests. We present evidence that pairs nesting at the extreme edge were forced to use suboptimal foraging areas (i.e. a semicircle of habitat), whereas interior pairs had a complete circle of suitable habitat in which to forage. Pied Flycatchers did not use clearcuts for foraging. Birds may try to com- pensate for suboptimal foraging area by increasing their food-search efficiency, or they may try to enlarge their foraging area by increasing its radius. Both strategies may increase the energy consumption of adults and the time spent searching for food, which may, in turn, decrease feeding frequency. However, we found no support for increased energy consump- tion. Nest-predation rate, food availability, and survival of parents were not associated with the distance of the nest from the edge. Our results indicate a harmful edge effect from forest fragmentation for Pied Flycatchers because offspring mass is related to fitness through brood survival to the next breeding season. Received 15 December 1997, accepted 31 October 1998.