Foraging niches of two passerines at their subarctic limit of distribution: the Siberian Tit Parus cinctus and the Pied Flycatcher Ficedula hypoleuca

Abstrakti

Foraging niches of a well-established native (Siberian Tit) and a southern migratory passerine (Pied Flycatcher) were studied at their northern limit of distribution in Finnish Lapland at 69°N. For both species, there were marked seasonal fluctuations in food availability, with peaks in late summer well after the breeding season. Overall, both species had wide and partially overlapping foraging niches during the breeding season . Extensive overlap of food niches is possible presumably because of the low density of birds in relation to their food resources. The overlap of foraging niches was lowest in late summer, at the time when food availability peaked . Niches were broadest in mid- (Siberian Tit) or late summer (Pied Flycatcher). A broad niche may be necessary for successful breeding since no single food source is available throughout the breeding season. This may make it impossible for truly specialized foragers to spread farther north because of the short period when its food sources are available.