Correlates of the change in ring ouzel turdus torquatus abundance in scotland from 1988–91 to 1999

Abstract

Aims To identify factors correlated with a population decline and range contraction between 1988–91 and 1999. Methods Regression models are used to describe the variation in Ring Ouzel abundance in 1988–91, and the change in Ring Ouzel abundance between 1988–91 and 1999. Results The abundance of Ring Ouzels in 1988–91 was negatively correlated with improved pasture, but positively with heather/smooth grass mosaic and Nardus/Molinia grassland. There was also a positive quadratic correlation with rock cover. A decline in Ring Ouzels between 1988–91 and 1999 was most likely on tetrads with shallow gradients, and outside of a 350–750 m altitudinal range. The change in ouzel numbers was also negatively correlated with both the initial area of conifer forest and heather/smooth grass mosaic. The rate of loss was greatest in those areas with a low Ring Ouzel abundance in 1988–91, although this effect was non-significant once habitat was accounted for. Conclusions The abundance of Ring Ouzels was linked to heather–grass mosaics, while declines were greater in tetrads lacking topographical features known to be selected by nesting ouzels. The negative relationship between forestry and population change suggests that large-scale afforestation of the uplands is a cause of concern. © 2003 British Trust for Ornithology.