20 April, 2022

Hawaiian endemic honeycreepers (Drepanidinae) are nectar robbers of the invasive banana poka (Passiflora tarminiana, Passifloraceae)

 by Seana Walsh, Richard Pender, and Noah Gomes

‘I‘iwi nectar robbing banana poka flowers in Hawai‘i.
Photo by Jack Jeffrey.

The establishment of species outside their natural ranges has led to interactions between species that did not evolve together. Understanding how pollination networks are affected by non-native species is useful for both invasive species management and native species conservation and restoration. Banana poka (Passiflora tarminiana) is a hummingbird pollinated liana native to South America. It is considered invasive in Hawai‘i where it has naturalized in higher elevation forests on the islands of Kaua‘i, Maui and Hawai‘i; habitats in which the remaining native forest birds, such as the Hawaiian honeycreepers, still occur. To develop an understanding of the interaction between banana poka and Hawaiian honeycreepers, we undertook a floral visitation study on the island of Hawai‘i where three nectarivorous honeycreepers and banana poka co-occur. Two honeycreeper species, ‘iiwi (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 floral tubes (60–90 mm long) which physically inhibits both honeycreeper species from accessing nectar via the front of the flower. In addition, the floral nectar traits of banana poka was assessed. Flowers produced large amounts of nectar containing high amounts of sucrose-dominant sugars. In contrast, based on the results of a fairly limited number of floral nectar studies, Hawai‘i’s bird pollinated plant species are believed to produce nectar that is dilute and rich in hexose sugars. 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.

Read the scientific publication in JPE.

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