(Drepanididae)
Class: Aves
Order: Passeriformes
Suborder: Passeri (Oscines)
Family: Drepanidinae
Thumbnail description
Small to medium, compact, finch-like, often brilliantly and variously colored birds with a wide variation of bill shapes and sizes
Size
3.9–8.3 in (10–21 cm)
Number of genera, species
21 genera; 51 species, including 13 subfossil and 15 extinct historically
Habitat
Forest
Conservation status
Critically Endangered: 6 species; Endangered: 5 species; Vulnerable: 7 species; Near Threatened: 5 species
Distribution
Endemic to the Hawaiian Islands
Evolution and systematics
Hawaiian honeycreepers are a splendid living textbook and gazetteer of adaptive radiation, or the evolution of many species, with varied characteristics, from one.
Establishing the relationships among the many genera and species of honeycreepers is ongoing and far from settled. As of 2002, ornithologists consider all honeycreeper species to be monophyletic, i.e., sharing one common ancestral species, probably a cardueline finch species from North America, a small flock of which reached the Hawaiian Islands sometime between 3 and 5 million years ago. Although the Hawaiian honeycreepers are as of 2002 often listed taxonomically as subfamily Drepanidinae within the family Fringillidae, the finches, for the purposes of this account they are treated as a separate family—the Drepanididae.
Once established in Hawaii, the founder species evolved and radiated explosively, filling empty ecological niches and producing a fantastically varied toolbox of bill forms for dealing with virtually every sort of food. Researchers have found fossils of honeycreepers as old as 120,000 years. Fossil ages in Hawaii are limited by the nature of the islands, which are volcanic and relatively transient in geological time.
Physical characteristics
Hawaiian honeycreepers are small to medium-sized, compactly built, finchlike birds, their plumage colors varying widely from dull olive green to brilliant yellow, crimson, and multicolors. The tongue is tubular in most species, with a fringed tip adapted to nectar feeding. Bill shapes and sizes vary enormously, and correlate directly with the foods favored by particular species. Some species retain stubby, cone-shaped, finchlike bills for generalized feeding on insects, seeds, and fruits. Others favor heavier, parrotlike bills for cracking seeds and chopping into especially tough food sources. The various sickle-billed species use their long, thin, downcurved bills to draw nectar from the depths of tubular and bell-shaped flowers. The akepa developed a bill with a crossed lower tip, which it uses like pliers. The Lanai hookbill sported a parrotlike bill with a sizeable gap between the two mandibles, for a function that will probably remain unknown.
Subfossil species had even more outrageous versions of the simple finch bill. Two species of shovelbills (genus Vangulifer), had bills that were long and thin but with broad, rounded tips. Unique among honeycreepers, these may have fitted the species out for snagging insects on the wing. The gapers (genus Aidemedia) had bills with powerful muscles for opening the bill against pressure. This trait has a parallel with the meadowlark (Sturnella sp.), which uses a gaping bill to force open sod for reaching earthworms. The extinct King Kong finch (Chloridops regiskongi) had the largest known honey-creeper bill. A reporter used the name "King Kong" as an adjective to convey the massiveness of the bill, and the comparison worked its way into scientific nomenclature.
Nearly all honeycreepers give off a strong, musky odor, which persists even in museum specimens.
Distribution
Honeycreepers are found only on the Hawaiian Islands. As considered here, the Hawaiian Islands include the familiar major islands, as well as a string of minor islets to the northwest of the main group, which includes Laysan Island, Nihoa Island, and the Pearl and Hermes Reef.
Habitat
Most honeycreepers are forest-dwellers. Exceptions include the Laysan finch (Psittirostra cantans) and Nihoa finch, which live on small, treeless islets. Although various species on the main islands originally lived throughout the lowlands as well as in the higher, mountainous areas, habitat loss and the proliferation of mosquitoes carrying avian disease now confines them mainly to mid-level and high tropical mesic (moist) forests and rainforests, 1,968 ft (600 m) above sea level and higher, most of them dominated by ohia trees (Metrosideros polymorpha). Some species prefer drier forests or a mix of dry, mesic, and rainforests. Many species depend on nectar from ohia flowers as a major or supplementary food source.
Behavior
The living honeycreeper species, despite their bewildering differences, share behavioral traits passed down from their finch-like ancestors.
All honeycreepers are diurnal. Individuals may be solitary foragers or forage in family groups, while some species show mixed-flock activity when foraging, especially when seeking out patches of ohia blooms, notably amakihis (Hemignathus spp.) and iiwis (Drepanis coccinea). Individuals of opposite sexes form strong pair bonds, and such pairings are monogamous and long-term for most species.
Honeycreepers produce a range of calls and songs as varied and distinct as the instruments of an orchestra, from ethereal music to coarse raspings. Calls and songs may vary even within a species. Some species stake out and defend nesting and feeding areas, other species tolerate intruders of their own or other species. Amakihis stake out breeding territories of 1–2.5 acres (0.4–1 ha), which they aggressively defend. The akohekohe (Palmeria dolei) is perhaps the scrappiest of all the honeycreepers in this regard.
Feeding ecology and diet
Honeycreepers eat almost anything edible, and run the entire gamut from generalist, omnivorous feeding, e.g., Laysan finches and amakihis, to specialization on a single plant species. Individual species tend to confine their diets to one or a few major sources. Foods include nectar of ohia (a primary food source for several species), insects, spiders, land snails, slugs, fruit, tree sap, seeds and seedpods, seabird eggs, and carrion. Species with long, curved bills poke them into flowers to reach nectar, while insect-grubbers pull or tear up epiphytic growth and bark to find arthropods. Species may pluck and eat fruit, break open seabird eggs, and cut or tear open seed pods. The po'o-uli (Melamprosops phaesoma) is unique among honeycreepers in preferring land snails as its main food, eating them shell and all. The Laysan and Nihoa finches have developed a taste for seabird eggs, which they peck or break open to get at the soupy innards.
Laysan finches have survived lean times by eating carrion of dead seabirds.
The finch-billed and parrot-billed honeycreepers can be roughly assumed under various genera: the Laysan and Nihoa finches; the palila (Loxioides); the Kona, Wahi, and King Kong grosbeaks (Chloridops); the greater and lesser koa finches (Rhodacanthis), the o'u (Psittirostra), the Lanai hookbill (Dysmorodrepanis); and the Maui parrotbill (Pseudonestor). Bills of these genera and species are short, strong, and finchlike or robust and parrotlike. They may generalize their diets like the Laysan finch, or specialize in getting at and eating tough foodstuffs like seedpods and hard seeds or tearing apart "structurally defended resources," such as arthropods hidden under tree bark or seeds in tough, fibrous pods. Females and young among the finch-bills and parrot-bills tend toward olive green or grayish green plumage, the males of some species add brighter shades of yellow, orange, and red to the basic olive or gray. The Maui parrotbill (Pseudonestor xanthophrys) uses its aptly named mouthpiece to rip into branches and stems; pluck and open fruit; and lift bark and lichen clumps to find, snag, and eat caterpillars and the larvae and pupae of beetles. The diet of the Kona grosbeak (Chloridops kona) was highly specialized, its main food source being the small, rock-hard seeds of the naio or bastard sandalwood tree (Myoporum sand-wicense). The bird used its massive, heavily muscle-powered bill to crack open the fruits.
Honeycreepers with long, narrow, downcurved bills are scattered among several genera: the curve-billed honeycreepers (Hemignathus), the sicklebills (Drepanis); and the alauahios (Paroreomyza). The bills become almost needlelike in some of these and can be half the length of the body, all for reaching nectar in the depths of ohia and other blossoms. Honey-creepers in the genus Hemignathus (amakihis, akialoas, nukupu'us, and akiapolaau) have a shorter lower mandible. Akiapolaau have a straight, thick lower mandible only half as long as the upper. This bird hammers audibly on tree bark with its lower mandible and plucks insects out of holes with the upper.
The amakihis, which are among the least specialized of the honeycreepers, take an wide food selection: caterpillars, plant lice, and spiders, which they uncover by probing leaves and twigs; nectar from ohia, lobelias, mamane, canna, and pritchardia palm; and non-native bananas and fuchsias.
Reproductive biology
Breeding takes place generally November through July, the males display to females, some species in groups resembling leks, and the sexes form strong, monogamous pair-bonds. Pairs build simple cup nests of twigs, lichens, and other plant materials on tree branches. As with all passerines, Drepanididae hatchlings are altricial, i.e., naked, blind, and helpless. The first young leave the nests anytime from the end of January through July and August. Only the female broods, while the male feeds the brooding female and both parents feed the chicks. The sexes of many honeycreeper species differ subtly or markedly in colors (sexual dichromatism), the males being more vividly and variously colored, the females tending to more cryptic coloration, favoring olive-greens and grays, although in some species both sexes have relatively plain rainment. A few species show sexual variation in size (sexual dimorphism), while some species show no sexual variation in size or color.
Conservation status
Fifteen species of Drepanididae have become extinct within historical times, mostly from loss of habitat through deforestation and environmental degradation. By IUCN standards, seven living species are Critical, five are Endangered, and three are Vulnerable. Nevertheless, all species are threatened to various degrees by a combination of loss of habitat, the introduction of mosquito-borne diseases of Culex quinquefasciatus, especially avian malaria (Plasmodium spp.) and avian pox, along with competition from and predation by invasive species. The o'u, Oahu alauahio (Paroreomyza maculata), and Maui nukupuu (Hemignathus lucidus affinis) may be extinct, none having been seen for several years. At the very cliff-edge of extinction is the po'o-uli, of which only three individuals remain.
At the opposite end of the scale, the amakihis are the most widespread, populous, and successful honeycreepers; their total population, all species, is estimated at an impressive 870,000. The several subspecies were formerly found on all the major islands. The iiwi, fairly common on the major islands, has a total population estimated at 340,000.
Significance to humans
Ancient Hawaiians made brilliant royal cloaks, mostly yellow and crimson, from thousands, if not millions, of tiny feathers of honeycreepers and other endemic birds of Hawaii. The practice has long been discontinued, but the honey-creepers earn their keep by pollinating ohia and other native plants and keeping the insect populations in check. Besides rendering those ecosystem services, they have become dependable ecotourism magnets. Their main value may be educational, as a visible, instructional living example of adaptive radiation. Finally, as poignant visions of endangered life, honeycreepers have become rallying symbols for conservation.
Species accounts
AkepaAkikiki
Akohekohe
Anianiau
Apapane
Greater koa finch
Lanai hookbill
Laysan finch
Palila
Po'o-uli
Resources
Books:Carlquist, Sherwin. Hawaii, A Natural History. New York: Natural History Press, American Museum of Natural History, 1992.
Denny, James. The Birds of Kauai Honolulu: University of Hawaii Press, 2001.
Hilton-Taylor, C., comp. 2000 IUCN Red List of Threatened Species. Species Survival Commission (SSC) Red List Programme. Cambridge, UK: IUCN 2000.
Poole, A., P. Stettenheim, and F. Gill, eds. Birds of North America: Life Histories for the 21st Century. (Monograph Series) Po'o-uli, no. 272; Akepa, no. 294; Apapane, no. 296; Maui Parrotbill, no. 311; Anianiau, no. 312; Iiwi, no. 327; Ou and Lanai Hookbill, no. 335–336; Amakihis, no. 360; Akohekohe, no. 400; Kona Grosbeak, Greater, and Lesser Koa-Finches, no. 424; Kakawahie and Oahu Alauahio, no. 503; Greater and Lesser Akialoa, no. 512; Akikiki, no. 552; Akiapala'au and Nukupuu, no. 600; Maui Alauahio, no. 681. Washington, DC: American Ornithologists Union, YEAR.
Pratt, H. Douglas, Phillip L. Bruner, and Delwyn G. Berrett. The Birds of Hawaii and the Tropical Pacific. Princeton, NJ: Princeton University Press, 1987.
Scott, J. M., S. Conant, and C. Van Riper III, eds. Evolution, Ecology, Conservation, and Management of Hawaiian Birds: A Vanishing Avifauna. Studies in Avian Biology 22. Camarillo, CA: Allen Press, Cooper Ornithological Society, 2001.
Stattersfield, Alison J., and David R. Capper, eds. Threatened Birds of the World: The Official Source for Birds on the IUCN Red List. Barcelona: Lynx Ediciones, 2001.
Periodicals:"Hawaii, Showcase of Evolution." Natural History 91, no. 12 (December 1982).
Olson, Storrs L., and Helen F. James. "Description of Thirty-Two New Species of Birds From the Hawaiian Islands; Parts I and II, Passeriformes." Ornithological Monographs 45&46, bound as one; American Ornithologists' Union, 1991.
Simon, Chris. "Hawaiian Evolutionary Biology: An Introduction;" Trends in Ecology and Evolution 2, no. 7 (July 1987): 175–178.
Simon, J. C., T. K. Pratt, K. E. Berlin, and J. R. Kowalsky. "Reproductive Ecology and Demography of the Akohekohe.;" Condor 103, no. 4:(Nov 2001): 736–745.
Organizations:The Bishop Museum. 1525 Bernice Street, Honolulu, HI 96817-0916 USA. Phone: (808) 847-3511. E-mail: museum@bishopmuseum.org Web site:
Pacific Island Ecosystems Research Center. 3190 Maile Way, St. John Hall, Room 408, Honolulu, HI 96822 USA. Phone: (808) 956-5691. Fax: (808) 956-5687. E-mail: Bill Steiner@usgs.gov Web site:
Payne, Robert B. "Bird Families of the World." University of Michigan Museum of Zoology, Bird Division. 12 Jan. 2000 (16 Mar. 2002).
Pratt, Thane. "Birds of Hawaii." Pacific Island Ecosystems Research Center. 18 June 2001 (16 Mar. 2002).
[Article by: Kevin F. Fitzgerald, BS]
