HAWAIIAN ENDEMIC HONEYCREEPERS (DREPANIDINAE) ARE NECTAR ROBBERS OF THE INVASIVE BANANA POKA (PASSIFLORA TARMINIANA, PASSIFLORACEAE)

Abstract

The human transport and subsequent naturalization of species outside their natural ranges has led to novel interactions between introduced and native species throughout the world. Understanding how introduced species impact pollination networks is useful for both invasive species management and native species conservation and restoration. Banana poka (Passiflora tarminiana), a hummingbird pollinated liana native to South America, has naturalized in higher elevation forests on the islands of Kaua'i, Maui and Hawai'i in the Hawaiian archipelago, habitats in which endemic honeycreepers still occur. To develop an understanding of the interaction between banana poka and honeycreepers, we undertook a floral visitation study at Hakalau Forest National Wildlife Refuge on the island of Hawai'i where three nectivorous honeycreepers and banana poka co-occur. Two honeycreeper species, 'i'iwi (Drepanis coccinea) and Hawai'i 'amakihi (Chlorodrepanis virens), nectar robbed all of the banana poka flowers that they visited, ostensibly due to the length of the corolla tubes (60–90 mm long) which physically inhibits both honeycreeper species from accessing nectar via the mouth of the corolla. In addition, the standing crop and sugar composition of banana poka floral nectar were assessed. Flowers produced large standing crops (375 ± 132 μL) of nectar containing 29.1 ± 1% (w/v) of sugar that was sucrose-dominant (mean: 95.6 ± 0.5% sucrose in each sample). Our observations suggest that the floral nectar of banana poka may form a substantial component of the diet of both honeycreeper species at the study site. Further research is needed to understand how infestations of banana poka affect bird pollination networks at this and other sites in Hawai'i.