Iiwi Life History

Habitat

Iiwi are forest birds strongly associated with native Hawaiian flowering trees. Historically they occurred from sea level (at least during winter storms) to the highest forests on the islands of Kauai, Oahu, Maui, Hawaii, Molokai, and Lanai. Currently, nearly the entire population is found in mountain forest on Hawaii, Maui, and Kauai between 1,300 and 1,900 meters (4,300 to 6,200 feet), with 1,300 meters being the present upper elevational limit of the malaria-carrying southern house mosquito. Iiwi occur primarily in forests with ohia lehua and koa trees and kolea, naio, and tree ferns in the understory. They are most abundant in areas where there are high numbers of ohia lehua and mamane in bloom.

Food

Iiwi feed mostly on nectar, but they also eat some insects and spiders, and have been observed feeding caterpillars to nestlings. Iiwi consume nectar mainly from the flowers of ohia lehua, mamane, and other native plants, and they also take advantage of the nectar from introduced plants like banana poka and tree alfalfa in some areas. These honeycreepers are restless foragers, visiting a flower for only a few seconds before moving onto the next. They typically stay in the middle to upper levels of the forest canopy, but they also forage lower when understory plants are in bloom. In addition to probing flowers, Iiwi use their bill to pierce the bases of tubular flowers.

Nesting

Nest Placement

In a breeding study on Kauai, all 14 nests discovered were placed in the crowns of ohia lehua trees, with an average height of 7 meters (23 feet).

Nest Description

A cup made mostly of twigs, with mosses, lichens, and bark fragments mixed in. The cup is lined mainly with lichens, with some shredded leaf or bark fibers.

Nesting Facts

Behavior

Iiwi are very conspicuous during the breeding season, with birds singing and calling frequently and males chasing other Iiwi away from nesting territories. They are strong fliers, with an undulating flight style typical of finches. Pairs appear to be monogamous within a breeding season. Both sexes help build the nest and feed the young, although females do most of the work for these activities. Only females incubate the eggs and brood the young. A nest typically contains two eggs, which hatch after 14 days. The chicks usually leave the nest after 21 days, but they can remain dependent on the adults for up to 4 months after they fledge.

Iiwi occur alone or in pairs during the breeding season, but during the rest of the year, they can occur in small flocks of up to nine birds. After the breeding season, Iiwi in a study on the island of Hawaii moved downslope from nesting areas to elevations below 1,200 meters (3,900 feet) —where malaria-carrying mosquitoes are present—before eventually moving back upslope, sometimes as high as 2,000–2,800 meters (6,600–9,200 feet). These movements seem to follow the peak blooming periods of the ohia, and at higher elevations, mamane.

When Iiwi occur together with other Hawaiian honeycreepers in ohia trees, they are dominant over Apapane and Hawaii Amakihi but are subordinate to Akohekohe. The aggression between Akohekohe and Iiwi is so strong that they usually have mutually exclusive territories. Interestingly, though, Iiwi often roost in large multi-species flocks with Apapane during the nonbreeding season.

Conservation

The International Union for Conservation of Nature lists Iiwi’s conservation status as Vulnerable and estimates the population size at 250,000–500,000 mature individuals. The Vulnerable status is based on a predicted population decline of 30–49% between 2020 and 2030 due to an increase in avian malaria resulting from climate change. The U.S. Fish & Wildlife Service lists Iiwi as Threatened under the Endangered Species Act.

Historically, Iiwi occurred from sea level (at least during winter storms) to the highest forests on the islands of Kauai, Oahu, Maui, Hawaii, Molokai, and Lanai. It no longer occurs on Lanai, and may be extirpated from Molokai and Oahu, although a small population is still thought to exist on Oahu. This species experienced an initial population decline in the 1890s and early 1900s, at a time when avian malaria became established in the Hawaiian Islands and the hunting of small birds with guns became popular.

The combination of avian malaria and climate change is the main current threat to the Iiwi. Avian malaria is lethal to about 94% of all Iiwi that contract it, leading to annual population declines of 16–20% in adults and 55–73% in juveniles. As of the early 2020s, 90% of all Iiwi lived between elevations of 1,300 and 1,900 meters (4,300 to 6,200 feet), with the lower limit determined by the upper elevational limit of both avian malaria and the southern house mosquitoes that transmit it. As temperatures increase due to climate change, mosquitoes will be able to survive at and carry malaria to higher elevations that are currently functioning as safe havens for Iiwi. For example, it's been estimated that a 2°C (3.6°F) rise in temperature could decrease Iiwi habitat by up to 96% in Hakalau Forest National Wildlife Refuge on the island of Hawaii. In addition, a new fungal threat, Rapid Ohia Death, has caused extensive mortality of ohia trees, one of the main sources of food and nest sites for Iiwi, and could ultimately infect about 40% of the ohia tree cover in Iiwi’s range.

Credits

Bird Banding Laboratory. North American Bird Banding Program Longevity Records. Version 2023.2. Eastern Ecological Science Center. US Geological Survey. Laurel, MD.

BirdLife International. 2020. Drepanis coccinea. The IUCN Red List of Threatened Species 2020: e.T22720844A179228794. https://dx.doi.org/10.2305/IUCN.UK.2020-3.RLTS.T22720844A179228794.en.

Fancy, S. G., C. J. Ralph, S. G. Mlodinow, and P. Pyle (2024). Iiwi (Drepanis coccinea), version 2.0. In Birds of the World (B. K. Keeney, Editor). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bow.iiwi.02

Lovette, I.J. (2019). Why evolution goes wild on islands: the science of adaptive radiation. Foldout insert in Living Bird 38(1). Available online at https://www.allaboutbirds.org/news/why-evolution-goes-wild-on-islands-the-science-of-adaptive-radiation/

Stokes, L. Q. and M. A. Young (2024). The Stokes Guide to Finches of the United States and Canada. Little, Brown and Company, New York, NY, USA.

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