Population decline of the Siberian Tit (Poecile cinctus) in southern Norway and an assessment of possible causes

Abstrakti

The Siberian Tit (Poecile cinctus) is an old-growth forest specialist in the northern taiga. The Finnish population has declined dramatically due to logging. An isolated population occurs in southern Norway. This population was estimated at 1,000 pairs based on surveys in 1979–80, and the Siberian Tit constituted 9% of all individuals in the whole bird community and 64% of all tits in lichen-dominated pine forest. In 2011–12 we censused tit species (Paridae) along 292.5 kmline transects at 51 sites in southern Norway with potential occurrence of Siberian Tit. We found that the Siberian Tit constituted only about 1% of all tit territories or individuals. Recensuses of two sites which had Siberian Tits in 1979–80 showed no presence in 2011. The overall distribution range appears to have contracted over the past 30 years, and we suggest that current population size is only 50–150 pairs. We suggest three possible causes (climate change, competition with other tit species, forestry) forwhy the population of Siberian Tits in southern Norway has declined.A prospective assessment of available evidence indicated that 1) therewas no change in elevation of historical records spanning > 40 years, 2) Great Tits (Parus major) andWillow Tits (Poecile montanus)were now common in areas where they did not occur in 1979–80, 3) there was a large overlap in habitat selection of the Siberian Tit and three other tit species, 4) there was only a weak association of Siberian Tits with old-growth forest, and 5) previously occupied sites had generally not been affected by logging. Thus, we suggest that future studies of population decline of the Siberian Tit should focus in particular on competitive interactions with other tit species.