The significance of morphological variation in the finch species on Gough, Inaccessible and Nightingale Islands, South Atlantic Ocean

Uni‐ and multivariate analyses were made of nine morphological characters on three species of finches Nesospiza acunhae (Inaccessible, Nightingale), N. wilkinsi (Nightingale) and Rowettia goughensis (Gough). The results of the univariate analysis were used to test four predictions about morphological changes with altered competitive backgrounds. Finch species that occur alone on an island or on an island where other finch species are rare have longer characters and more variable character distributions. A multivariate analysis of six bill characters showed that the bill of Rowettia is more similar to that of acunhae than either is to wilkinsi. A multivariate analysis on wing length, tarsus length and hallux length shows that Rowettia is morphologically closer to wilkinsi than it is to acunhae. It is suggested that nothing is gained by treating the Gough I. finch as belonging to a monotypic genus.