WEATHER AND BREEDING SUCCESS AT HIGH-LATITUDES - THE PIED FLYCATCHER FICEDULA-HYPOLEUCA AND THE SIBERIAN TIT PARUS-CINCTUS

The breeding success of the migratory Pied Flycatcher (Ficedula hypole uca) and the resident Siberian Tit (Parus cinctus) were studied during 1986-1994 in Finnish Lapland. In the Pied Flycatcher, 15% of eggs did not hatch. In spells of cold weather, during the nestling period, Pie d Flycatchers tried to compensate for the inactivity of winged insects (main food items) by altering their foraging niches and diet. However , low temperatures greatly decreased the feeding frequency of the Pied Flycatcher. The incapability to feed the young in cold and rainy cond itions negatively affected nestling growth and fledging success in the Pied Flycatcher. In the Siberian Tit, neither the foraging strategy, nor the feeding frequency changed in relation to temperature. The hatc hing success of the Siberian Tit was very good in spite of early breed ing, but 22% of nestlings died during the nestling period. We could no t link nestling mortality with any climatic factors.