Importance of Sitka Spruce Picea sitchensis seed and garden bird-feeders for Siskins Carduelis spinus and Coal Tits Periparus ater

Abstract

Capsule Siskins and Coal Tits were present in gardens more often in years of poor Sitka Spruce cone crops, with synchrony across the UK. Aims To examine how the relative abundances of Siskins and Coal Tits in a garden in western Scotland varied annually with the size of the spruce cone crop, and to determine whether this pattern was similar nationally. Methods A ten-year mist-netting data set from Tarbet, Argyll and Bute was used to test the hypothesis that some species utilize supplementary food in gardens more often in years with poor cone crops than in years when crops are large. Annual peaks in the relative abundances of four species (two that ate conifer seed and two that did not) in Tarbet were correlated with a Sitka Spruce masting index. BTO Garden BirdWatch data from six regions of the UK were correlated with the Tarbet data, the cone index and each other to determine the extent of synchrony. Results Both Siskins and Coal Tits were present more often in the Tarbet garden in years with poor cone crops, with relative abundances significantly negatively correlated with cone crop for both species (r = −0.739 and −0.832, respectively). Correlations between regions using BTO data showed abundances of species in gardens to be broadly similar across the UK. Independent scores of cone abundance in Kielder and Galloway were correlated. Correlations between BTO data, cone index and Tarbet garden data were mostly high and almost all in the same direction, also indicating a degree of synchrony in cone production across the UK. Conclusion Both Siskins and Coal Tits appear to be influenced by changes in cone abundance, switching to feed on supplementary food in gardens more often in years with few cones than in mast years. While such a relationship has been shown previously for Siskins, for Coal Tits this is a novel result.