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The Hawaiian Honeycreepers (subfamily Drepanidinae of family Fringillidae; sometimes treated as family Drepanididae) evolved and diversified in the Hawaiian Archipelago from a single ancestral colonist, almost certainly a cardueline finch resembling modern-day redpolls, goldfinches and siskins (Carduelis), or their close relatives. This group represents a classic example of adaptive radiation and when scientists first encountered the species from this radiation in the late 1700s, they were initially assigned to several different bird families based on their diverse morphology, behavior, and ecology. An unusual and important clue to their common ancestry was a shared distinctive musty aroma, apparent in both live birds and dead specimens, that was first reported in the literature by R.C.L. Perkins, a pioneering investigator of Hawaiian biodiversity. Morphological, behavioral, paleontological, and genetic investigations have now firmly established the monophyly of this group.
This group includes nearly two dozen extant species and at least 16 additional species that have gone extinct since 1600. These are small to medium sized (10-19 cm) passerines with highly varied morphology and colors ranging from dull olive green to bright red or yellow. Various honeycreeper species are found in wet and dry forests and even in atoll vegetation.
As a group, the Hawaiian Honeycreepers have not fared well in the face of human colonization of Hawaii. By the time Europeans first visited the islands, in 1778, virtually all the lowlands had been deforested, seabirds were breeding only on offshore islets, and half of the avifauna present prior to settlement by seafaring humans (Polynesians), including many honeycreepers, had already been driven to extinction. A rich record of non-mineralized "sub-fossils", some with recoverable DNA, has revealed that numerous honeycreeper species went extinct following Polynesian colonization of Hawaii but prior to European discovery of the islands. The arrival of Europeans unleashed a new wave of honeycreeper population declines and extinctions, mainly due to the introduction of alien species such as cattle, goats, and pigs, whose feral descendants devastated native habitats, as well as rats, cats, rabbits, and other species. The catastrophic surge of honeycreeper declines and extinctions that began in the late 19th century and continued into the 20th century was mystifying for decades, but has now been attributed in large part to avian malaria and avian pox transmitted by introduced mosquitos. The mosquitos were apparently established prior to the inadvertent delivery of the avian malaria parasite (Plasmodium relictum) in the blood of introduced birds.
As of 2010, all but two of the drepanidine species that survived into the 1980s were globally threatened, including nine that were critically endangered (several of these may already be extinct). The challenges faced by those working to conserve and recover honeycreeper populations are daunting, and the losses already behind us are tragic, but substantial tracts of suitable habitat are now protected and successful captive breeding programs for several species may buy time as investigators look for effective ways to protect the birds from disease.
Comprehensive reviews of the biology of this family have been provided by Pratt (2005, 2010); Pratt (2009) has compiled recordings of the songs and calls of Hawaiian honeycreepers.
(Pratt 2010 and references therein)