Because it is so poorly known, the honeycreeper family, in particular its extinct members, arouses a certain amount of controversy. It is classified and reclassified over and over again, and drastic revisions of the family are made from time to time. Unfortunately, these revisions are, of necessity, made from specimen material rather than from any real recourse to the living birds. For this reason these revisions should be viewed with a certain degree of caution. They tend to be prone to the whims and prejudices of individuals, and also subject to the dictates of fashion.
In no case is this better exemplified than in the instance of the Akialoa. Perhaps the Akialoa constitutes one species, perhaps two, perhaps even four. It has been divided into two, a “Greater” and a “Lesser”, and into four with each inhabited Hawaiian island being held to have its own species. The specimen material is very difficult to interpret, however. The forms from Lanai (lanaiensis) and O’ahu (ellisianus) are known only from very, very few specimens, so there is no real series on which to base conclusions. The other two forms, nominate obscurus from Hawaii and procerus from Kauia, are known from rather more skins, but even in these cases comparisons are clouded by various factors. The main problem is that the Akialoa was a generally variable bird and individuals of each kind show some overlap in terms of size and colour. It is possible that individuals became brighter in colour when they were breeding, although it should be said that there is no real evidence of this. Bill length is held to be a significant character, but this too is variable: there is evidence to show that towards the end of its existence as a species, the Akialoa’s beak tended to be rather shorter than in earlier years. Perhaps this was because the birds were generally in poor health, and collectors who took specimens during the 1890’s noticed that individuals were often covered in sores, tumours and swellings, particularly on the head and feet; or maybe the new circumstances on the islands were inhibiting proper growth.
The most sensible way forward is, perhaps, to regard the Akialoa as a single species with four races. Bearing in mind the paucity of specimen material available, no other course seems meaningful. However they may be interpreted, the birds that are known as Akialoas were among the most intriguing of the honeycreepers. The extraordinarily delicate beak is in complete contrast to the shorter, stumpy bills of the Koa Finch and the Kona Grosbeak. The lower mandible was often considerably shorter than the upper, and with this strange device individuals were able to suck nectar from the flowers of ohias and lobelias, and they could also probe into cavities for insects and their larvae. R. C. L. Perkins noticed them clinging to tree trunks like “true” creepers when they were feeding. While it is known that there were Akialoas on Hawaii, O’ahu, Lanai and Kauai, it is quite possible that birds were present on other islands. It is surprising to find, for instance, that they were never reported from Molokai and Maui. Perhaps they vanished from these islands at a comparatively early date. It is likely that the Akialoas from Oahu became extinct around 1840, although there are claimed records, made by experienced ornithologists, of possible sightings made during the late 1930’s. The Lanai and Hawaii populations disappeared around 1900, but Kauai birds held out for much longer. Their stronghold was the same Alaka’i Swamp that was home to the last Kauai ‘O’os. A few individuals were still in existence during the early 1960’s but the last record of them seems to date from 1967.
The obvious frailty of the Akialoa reflects the fragility of the honeycreepers as a whole. In addition to all the other factors that depleted them, the danger that the mosquito posed cannot be overstated. Once this insect arrived in the Hawaiian Islands, birds that lived at lower altitudes were seriously affected by the bites of these creatures. Even those species living at altitudes that were unattractive to mosquitoes could be vulnerable. Sometimes they would descend to lower levels to ride out the effects of hurricanes, and then the bites could prove fatal. Captive birds that have been brought down from altitude have been observed to die within minutes of sustaining a bite.
Syst. Nat. 1(1): 470.