Hawaiian honeycreeper Hawaiian honeycreepers are a group of small, passerine birds endemic to Hawaii. They are closely related to the rosefinches in the genus ''Carpodacus'', but many species have evolved features unlike those present in any other finch. Their great ...

s (

Fringillidae The true finches are small to medium-sized passerine birds in the family Fringillidae. Finches have stout conical bills adapted for eating seeds and nuts and often have colourful plumage. They occupy a great range of habitats where they are usua ...

), of the subfamily

Carduelinae The cardueline finches are a subfamily, Carduelinae, one of three subfamilies of the finch family Fringillidae, the others being the Fringillinae and the Euphoniinae. The Hawaiian honeycreepers are now included in this subfamily. Except for the ...

, were once quite abundant in all forests throughout

Hawai'i Hawaii ( ; haw, Hawaii or ) is a state in the Western United States, located in the Pacific Ocean about from the U.S. mainland. It is the only U.S. state outside North America, the only state that is an archipelago, and the only ...

. This group of birds historically consisted of at least 51 species. Less than half of Hawaii's previously extant species of honeycreeper still exist. Threats to species include habitat loss, avian malaria, predation by non-native mammals, and competition from non-native birds.

Hawaiian honeycreeper threats

The honeycreepers are threatened by recently introduced

predation Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill th ...

competition Competition is a rivalry where two or more parties strive for a common goal which cannot be shared: where one's gain is the other's loss (an example of which is a zero-sum game). Competition can arise between entities such as organisms, indiv ...

, parasitism, degradation of habitat, and

infectious disease An infection is the invasion of tissues by pathogens, their multiplication, and the reaction of host tissues to the infectious agent and the toxins they produce. An infectious disease, also known as a transmissible disease or communicable di ...

including

mosquito Mosquitoes (or mosquitos) are members of a group of almost 3,600 species of small flies within the family Culicidae (from the Latin ''culex'' meaning " gnat"). The word "mosquito" (formed by ''mosca'' and diminutive ''-ito'') is Spanish for "li ...

-borne

avian malaria Avian malaria is a parasitic disease of birds, caused by parasite species belonging to the genera '' Plasmodium'' and '' Hemoproteus'' (phylum Apicomplexa, class Haemosporidia, family Plasmoiidae). The disease is transmitted by a dipteran vecto ...

. One of the consequences of the invasive birds is the introduction of avian malaria. The pathogen is primarily transmitted via female mosquitoes who will pass on the disease by biting a

susceptible individual In epidemiology a susceptible individual (sometimes known simply as a susceptible) is a member of a population who is at risk of becoming infected by a disease. Susceptible individuals Susceptibles have been exposed to neither the wild strain ...

after having bitten an infected individual. The main mosquito vector (''Culex quinquefasciatus'') was introduced over a hundred years before the pathogen (''Plasmodium r. capistranoae''), mostly hosted by the blue-breasted quail (''Excalfactoria chinensis''). Later, two other mosquito species, the Asian tiger mosquito (''Aedes albopictus'') and the bromeliad mosquito (''Wyeomyia mitchellii'') were introduced to the islands. The

immune system The immune system is a network of biological processes that protects an organism from diseases. It detects and responds to a wide variety of pathogens, from viruses to parasitic worms, as well as cancer cells and objects such as wood splint ...

of the honeycreepers had not been exposed to avian malaria since its common ancestor existed 4 to 5 million years ago. Thus, the honeycreepers had not co-evolved with the pathogen to develop resistance as those birds on the mainland did. In the 1970s, the Hawai’i Forest Bird Survey found that native birds had retreated from mid or low elevation forest and had been replaced by exotic species; however, competition was not documented between them and the native species. During the same time, the elevational limit of malaria was established to be approximately Above this elevation the mosquito vector could not subsist due to the low temperatures. Due to malaria, highly susceptible species must reside at .

Global warming In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to E ...

may move that line higher until these species no longer have a refuge. Degradation of habitat for the Hawaiian honeycreepers has also been a main cause for the radical decrease in their population numbers. Colonization of the Hawaiian islands has led to extensive

deforestation Deforestation or forest clearance is the removal of a forest or stand of trees from land that is then converted to non-forest use. Deforestation can involve conversion of forest land to farms, ranches, or urban use. The most concentrated ...

to make way for

agriculture Agriculture or farming is the practice of cultivating plants and livestock. Agriculture was the key development in the rise of sedentary human civilization, whereby farming of domesticated species created food surpluses that enabled people t ...

ranch A ranch (from es, rancho/Mexican Spanish) is an area of land, including various structures, given primarily to ranching, the practice of raising grazing livestock such as cattle and sheep. It is a subtype of a farm. These terms are most ofte ...

ing, and other development. Furthermore, where the forests are still intact, introduced

domestic pig The pig (''Sus domesticus''), often called swine, hog, or domestic pig when distinguishing from other members of the genus '' Sus'', is an omnivorous, domesticated, even-toed, hoofed mammal. It is variously considered a subspecies of ''Sus ...

s and

goat The goat or domestic goat (''Capra hircus'') is a domesticated species of goat-antelope typically kept as livestock. It was domesticated from the wild goat (''C. aegagrus'') of Southwest Asia and Eastern Europe. The goat is a member of the a ...

s have done considerable damage to habitat. Other destructive invasive species include

cat The cat (''Felis catus'') is a domestic species of small carnivorous mammal. It is the only domesticated species in the family Felidae and is commonly referred to as the domestic cat or house cat to distinguish it from the wild members of ...

s, who feed on birds, especially those who are naive to predators (such as Hawaiian honeycreepers). Efforts to conserve the remaining species are of great interest and a couple of different methods have been described.

Remove mosquito vector

There are a few strategies for mosquito removal which include the reduction of mosquito breeding sites by: chemical and biological control agents, genetic manipulation of the population, and removal of feral

ungulate Ungulates ( ) are members of the diverse clade Ungulata which primarily consists of large mammals with hooves. These include odd-toed ungulates such as horses, rhinoceroses, and tapirs; and even-toed ungulates such as cattle, pigs, giraffes, ...

s from critical forest habitats. The goal is to eliminate the mosquito populations using

herd immunity Herd immunity (also called herd effect, community immunity, population immunity, or mass immunity) is a form of indirect protection that applies only to contagious diseases. It occurs when a sufficient percentage of a population has become im ...

, which does not require the unfeasible eradication of every individual mosquito. Another strategy requires releasing genetically manipulated sterile mosquito males into the wild every generation and as a consequence the mosquito populations diminish over time.

Captive breeding

In many cases

habitat protection Habitat conservation is a management practice that seeks to conserve, protect and restore habitats and prevent species extinction, fragmentation or reduction in range. It is a priority of many groups that cannot be easily characterized in term ...

is not occurring fast enough for critically endangered Hawaiian honeycreeper species to keep their populations afloat. The Zoological Society of San Diego and Peregrine Fund have established management programs aimed at breeding these species in captivity and releasing them back into the wild.2000 Hawaiian Endangered Bird Conservation Program, Annual Report to: USFAW/DOFAW/KSBE/BRD/ZSSD/TPF As reported in 2000, the major challenge for the program did not include successfully breeding the birds in captivity but finding suitable habitat to release them. Thus, habitat management and restoration must be rigorously ensured before this breeding program can be secured.

Clearing habitat of invasive species

The Hawaiian honeycreepers are generally specialists both in diet and in habitat. This has left them very vulnerable directly and indirectly to the

generalist A generalist is a person with a wide array of knowledge on a variety of subjects, useful or not. It may also refer to: Occupations * a physician who provides general health care, as opposed to a medical specialist; see also: ** General pract ...

invaders that have been introduced to the islands. Other birds have provided direct competition for resources with the honeycreepers as well as brought disease (such as avian malaria). However removing the introduced birds is difficult due to their inaccessibility to humans and high dispersal ability. Introduced ungulates include

pig The pig (''Sus domesticus''), often called swine, hog, or domestic pig when distinguishing from other members of the genus '' Sus'', is an omnivorous, domesticated, even-toed, hoofed mammal. It is variously considered a subspecies of ''Sus ...

s and

s. Removal of large vertebrates requires both fencing and direct removal of the animals. In places where pigs have been removed, vegetation has begun to recover. However, Hawaiian honeycreeper numbers are still in decline and this may be due to introduced predators:

feral A feral () animal or plant is one that lives in the wild but is descended from domesticated individuals. As with an introduced species, the introduction of feral animals or plants to non-native regions may disrupt ecosystems and has, in some ...

small Asian mongoose Small Asian mongoose is a common name applied to two mammals which were formerly considered to be a single species: * Javan mongoose *Small Indian mongoose The small Indian mongoose (''Urva auropunctata'') is a mongoose species native to Iraq an ...

s, and three species of rat.

Hope: the ʻamakihi

The common ʻamakihi (''Hemignathus virens'') is one of seven extant honeycreeper species on Hawai’i Island. It is a small generalist that has historically shown high mortality rates due to infection by

. Surprisingly, they have been found at altitudes below despite their exposure to the pathogen. 90% of these birds showed they had contracted and survived the disease. This finding has raised the possibility that the species may be evolving resistance to malaria, however this may be only a localized event.

References