Severe alpine weather, prey availability and reproduction in two species of passerine: A test of the permanent prey availability hypothesis

The permanent prey availability hypothesis predicts that permanent availabi lity of food concentrated in low vegetation facilitates the survival of off spring of insectivorous passerines that breed in alpine ecosystems during h arsh weather conditions. We tested this hypothesis by examining prey availa bility in good and bad weather conditions in the meadow pipit (Anthus prate nsis), which breeds on alpine slopes and by examining the stomach contents of dead meadow pipit and pied flycatcher (Ficedula hypoleuca) nestlings in the Jeseniky mountains (in the Czech republic) in 1993-1997. Despite freque nt harsh weather, only 9.6 % (n = 40) of meadow pipit nestlings died during prolonged cold and rainy periods. Fast cooling in snowstorms and liver and kidney dysfunction during long cold and rainy periods seemed to be the maj or causes of death. Starvation appeared to play a minor role in causing nes tling mortality, because the stomachs of dead chicks were mostly filled wit h food. In contrast, the majority of pied flycatcher nestlings died (28.6 % , n = 24) by starvation, indicated by the fact that stomachs of dead nestli ngs were empty. Abundance, taxonomic composition, and average body length o f potential prey (registered by sweep-netting in low vegetation) were simil ar during periods of cold, and warm weather (low, and high insect activitie s). Although the density of prey available to meadow pipits decreased with time of breeding season, there was no difference in prey availability in go od or bad weather for early or late nests. Thus, the results supported the permanent prey availability hypothesis.