Habitat preference and breeding performance in four hole-nesting passerines at the northern limit of their range

Abstrakti

Habitat preference and its relation to breeding performance were studied with reference to two contrasting hypotheses: 1) birds at edge of their range select the optimal habitat, and 2) the birds are unselective as to habitat characteristics, because habitatindependent factors (e .g . weather) rule out any benefit from careful habitat selection . No preference for vegetational characteristics (dominant tree, field layer vegetation) was observed in the Siberian and Great Tits or the Redstart. This suggests that these species are less selective of those characteristics than in more southern regions . The Pied Flycatcher preferred birch forests at low altitudes, but pine forests at high altitudes . In two cases, however, other characteristics affected habitat selection: Redstarts preferred low altitude sites andGreat Tits bred more often close to human settlement. Sites at the highest altitudes were avoided by the other species as well . Breeding success correlated positively with the habitat preference . Asweanalysed data from several years, this suggests that differences in habitat quality are fairly constant in spite of wide variation in weather conditions . The preferred habitats probably contain some food resources that are not completely governed by the weather conditions . Clutch size was affected by habitat only in the Siberian Tit, which suggests adjustment ability in this northern species .