Sexing juvenile Siskins Spinus spinus in southeast England

Abstract

In this report we test the proposal that the length of the black blotch on the second outermost rectrix is a useful criterion for sexing Siskins in juvenile plumage. In total, 451 individuals at Leith Hill, southeast England, were sexed after their post-juvenile moult on the basis of body plumage and the length of the black blotch measured. Differences in blotch length between males and females were statistically significant. These results suggest that Siskins in juvenile body plumage with a black blotch measuring >30 mm can be sexed as females, and <27 mm as males.