Effects of trophic morphology and behavior on foraging rates of three Hawaiian honeycreepers

Summary

The effects of trophic morphology and behavior of three Hawaiian honeycreepers (Fringillidae: Drepanidinae) upon their foraging rates on the flowers of Vaccinium calycinum are examined. The Maui Creeper (Paroreomyza montana), the Amakihi (Hemianathus virens), and the I'iwi (Vestiaria coccinea) show shifts from a short straight bill to a long decurved bill, from a tongue adapted for insect feeding to one specialized for nectar, and diets ranging from primarily probing for insects to primarily nectarivorous. This diversity is examined feeding on the simple straight tubular corollas of the Vaccinium. Significant differences (P<0.001, t-tests) exist among the birds with respect to foraging rates on these flowers. The I'iwi, with its greatly decurved (64°) bill feeds the quickest (2.09 s/flower) while the Maui Creeper with its rather straight (18°) bill feeds the slowest (3.87 s/flower). These differences are seen to be the result of differing abilities of tongues to extract nectar as well as differing behavioral tactics of floral exploration and nectar extraction. This suggests that predictions of foraging efficiency based solely on bill morphology are not necessarily valid, and that other factors (tongue morphology, foraging maneuvers, and typical food spectrum) must also be considered.