Evaluating ‘I‘iwi Responses to Nectar Availability and Habitat Quality

Science Center Objects

‘I‘iwi  populations have severely declined in recent decades in Hawai‘i Volcanoes National Park (HAVO) and elsewhere in the Hawaiian Islands due to the cumulative impacts of many invasive threats that have degraded habitats, disrupted food webs, competed for resources, depredated nests and birds, and transmitted diseases.

‘i‘iwi on a mamane
‘I‘iwi on māmane. Photo: C. Heliker
Adult and juvenile iiwi side by side
Adult and juvenile ‘i‘iwi. Photo: C. Squibb

Overview:

 ‘I‘iwi  (Vestiaria coccinea) populations have severely declined severely in recent decades in Hawai‘i Volcanoes National Park (HAVO) and elsewhere in the Hawaiian Islands due to the cumulative impacts of many invasive threats that have degraded habitats, disrupted food webs, competed for resources, depredated nests and birds, and transmitted diseases. Although feral pigs and goats have been removed from important bird habitats within HAVO, native vegetation is slow to recover from long-term browse damage and additional management is needed to prevent i'iwi from becoming extirpated.

‘I‘iwi feed primarily on nectar, and some travel far to exploit locally abundant sources. Understanding the responses of ‘i‘iwi to nectar availability will help managers develop strategies for attracting i'iwi from marginal or high-risk habitats and retaining them in protected areas.  For this purpose, information is needed concerning the response of i'iwi to various floral nectars and about the structure and composition of the vegetation, temporal availability of nectar across the landscape, quality of nectars, and the interactions of ‘i‘iwi with other nectar-feeding bird species.

Project Objectives:

‘ōhi‘a lehua
‘Ōhi‘a lehua in bloom. Photo: J. Jacobi

The primary objective is to determine how the availability and quality of nectar resources might be managed to influence ‘i‘iwi to remain longer in protected habitat. More specifically, we will identify patterns of resource use by i'iwi through observation and by manipulating the availability and quality of nectar. We also will evaluate competitive interactions for nectar resources among ‘i‘iwi and other forest birds. Habitat structure and composition and the phenological patterns of plant species will be investigated to evaluate the temporal and spatial distribution of nectar. The quantity and quality (i.e., sugar composition) of nectar available to ‘i‘iwi will be determined. We also will consider the management implications of restoring habitat for the benefit of ‘i‘iwi within HAVO.

Highlights and Key Findings:

We established that low numbers of i'iwi permanently reside and breed in HAVO at upper elevations in the Mauna Loa region and that dense, multi-species patches of trees are preferred habitats. Our observations indicated that heavy rainfall likely caused the abandonment of two eggs, causing the pair to re-nest. A small number of apparent immigrants from adjacent lands appeared in the study area during the māmane flowering season. ‘I‘iwi shifted their feeding activity between māmane and ‘ōhi‘a as flower abundance changed; blooming peaks were offset by 4-5 months. ‘I‘iwi and other bird species in the wild were attracted to a nectar mimic composed exclusively of sucrose, providing a means for manipulating resource levels to evaluate changes in ‘i‘iwi behavior. In aviary trials, Hawai‘i ‘amakihi were more attracted to nectar mimics that were high in sucrose. Measurements of blood glucose levels indicated that they were able to metabolize the sucrose. Nectar of ‘ōhi‘a was low in sucrose, but māmane nectar was relatively balanced between sucrose, glucose, and fructose. Nectar of an introduced species that is highly attractive to ‘i‘iwi was sucrose-rich. We planted four rare endemic mint species (Phyllostegia stachyoidesStenogyne rugosaS. angustifolia, and Haplostachys haplostachya) and ‘ākala that were propagated by HAVO. The mint species were planted in the breeding territory of a pair of ‘i‘iwi to evaluate their use of species that have been absent for decades due to browsing by introduced ungulates. We deployed an automated watering system to help the plants establish their root systems during a persistent drought.