PATTERNS OF MORPHOMETRIC VARIATION IN BIRDS TAILS - LENGTH, SHAPE ANDVARIABILITY

In Palaearctic birds, tail length was more variable than wing-and tars us, but not bill lengths. Tails of the ornamental shapes pin, lyre and graduated varied more in length than did nonornamental shapes. Log co efficient of variation (CV) tail length showed an overall U-shaped rel ationship with longtailedness, but although the CV for most tail shape s increased in short-tailed species, only in ornamental shapes was CV also high in long-tailed species. CV of fork depth was lowest at a for k depth of 2, and considerably higher in shallow forked tails. CV stre amer lengths were similar to CV deep fork depths. The more deeply fork ed tails thus seem ornamental. Phylogenetically independent contrasts confirmed in males, but not females, that long-tailed species had grea ter CV than medium-railed species, and the greater CV of graduated tha n square tails, but the CV of short-and medium-tailed species did not differ. These comparisons, however, did not control for tail shape. Th e greater elongation and CV of tails with ornamental shapes are consis tent with an influence of sexual/signal selection on these tails, and the increase in CV with longtailedness suggests that Weber's law appli es to the perceptual threshold for tail length. Sexual selection may h ave a widespread, hut moderate, influence on tail traits in birds. (C) 1997 The Linnean Society London.