EVOLUTIONARY CONSEQUENCES OF EXTINCTIONS IN POPULATIONS OF A HAWAIIANHONEYCREEPER

We report on the evolutionary change in bill size of a species of Hawa iian honeycreeper resulting from an apparent dietary shift caused by d ramatic declines and extinctions of lobelioids, a historically favored nectar source. Although it now feeds mainly on the flowers of the obi a tree (Metrosideros polymorpha), early Hawaiian avifaunal accounts re port that the i'iwi (Vestiaria coccinea), which has a long decurved bi ll fed primarily on the flowers of Hawaiian Lobelioideae, which typica lly have long decurved corollas. A coevolutionary association of i'iwi bill and flower morphology has often been asserted We test the hypoth esis that the shift in the i'iwi's diet from the long corolla lobelioi d flowers to ohia flowers, which lack corollas, resulted in directiona l selection for shorter bills. We evaluate this hypothesis by comparin g the morphological characters of museum specimens from the island of Hawaii collected before 1902 with recent specimens from the Hakalau Na tional Wildlife Refuge, Hawaii. We examine evidence of change in morph ological characters using multivariate analysis and a nonparametric cu bic spline technique. Results from all analyses are congruent bill len gth is shorter in recent specimens.