Tail length in birds in relation to tail shape, general flight ecology andsexual selection

Relative tail length (longtailedness) of Palearctic birds was assessed by t he standardized residuals of log-log regressions of tail length on wing len gth and tarsus length. The mean degree of tail shortening was greater than mean degree of tail lengthening but there was a greater frequency of extrem e long-tailed than short-tailed species. Longtailedness was greater in orna mental pin, lyre, deep forked and graduated shaped tails. These shapes (exc ept graduated, for which data were lacking) were also relatively long-taile d according to shortest-rectrix lengths, this extra length potentially cont ributing compensatory lift. In forked tails, tail ratio increased linearly with longtailedness to above the aerodynamic optimum, and thus the most elo ngated forked tails were also more deeply forked. Tail shortening was marke d for rounded tails, a surprising result in view of their slightly ornament al shape. Phylogenetically independent contrasts showed significantly great er longtailedness in graduated than square-tailed species, confirming the s pecies-wide analysis. Ln phylogenetically independent contrasts of longtail edness and ecological factors, short-tailed species had significantly great er flight distances than medium-tailed species, but long- and medium-tailed species did not differ in migratory distance, foraging distance, overall f light distance or importance of aerial foraging. The data suggest that ecol ogical factors, i.e, natural selection, are more important in the evolution of short-tailedness than longtailedness in birds, and that an additional i nfluence of sexual selection on tail length and shape is also widespread.