Intraspecific Variation in Wing Length and Male Plumage Coloration with Migratory Behaviour in Continental and Island Populations

Abstract

Interspecific comparisons have previously shown both a dullness in male plumage and a reduction in wing length of both resident and island species compared with migratory and continental species, respectively. Intraspecific comparisons between subspecies were used to investigate whether these differences also occur within races of the same species and whether the effects of migration and island endemism are separate and additional, or identical, island endemics being resident. Continental migrant subspecies had both more colourful male plumage and longer wings than continental resident subspecies. Continental resident subspecies were longer winged and tended to be more colourful than island resident subspecies. No difference in either coloration or wing length was found between continental migrant and island migrant subspecies. In a three-way comparison, the order continental migrant > continental resident > island resident was supported for both wing length and plumage coloration. Intraspecific variation therefore parallels interspecific variation in male plumage coloration and wing length, and the trait reduction in island subspecies is additional to the reduction associated with residency, but conditional on lack of migration. Possible differences in natural and sexual selection pressures on coloration ensuing from insular and migratory life styles are discussed.