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Description

A selection of recently extinct fauna from the Hawaiian Islands, to scale.

Although politically part of the USA, the Hawaiian Islands (HI) are an archipelago of 8 main islands and many smaller ones, situated in the North Pacific over 3600 kms from the North American continent. Volcanic in origin, the environments on the islands varies considerably between tropical lowland and cool alpine on the peaks. Due to their isolation, very few animal groups were able to colonise the islands and consequently there is a high degree of endemism in the fauna and flora.

As with many of the remote island groups in the Pacific, humans were very late in colonising the HI. Polynesians first made landfall sometime between 124 and 1120 AD, while the first Europeans didn't arrive until 1542 (Spanish explorers). It was only following the 1778 visit by British explorer Captain James Cook that Europeans finally established colonies on the islands. As usual human contact brought an immediate impact with habitat clearing and the introduction (deliberate/accidental) of a wide array of pest species. In addition many species were hunted in large numbers as specimens for the amateur/museum collection trade. Many native birds were flightless or naive towards predators, and as a result the HI has experienced one of the highest extinction rates globally. There will be several posts to cover the extinct vertebrate fauna (mostly birds) of the HI; this one will focus on the endemic Hawaiian honeycreepers.

Quite feasibly, the honeycreepers of the HI represent the most impressive example of adaptive radiation among vertebrates. Despite the name, they were not closely related to the true Neotropical Cyanerpes honeycreepers which are specialised tanagers (Thraupidae). However prior to molecular studies, it was uncertain as where the origins of Hawaiian honeycreepers lay. Previously they had been placed in their own family ('Drepanidae'), linked to the American sparrows/buntings, and finally are now considered a very specialised branch of the cardueline finches within the Fringillidae or true finches. The honeycreepers split from their closest living relatives, the Eurasian rosefinches, between 7 and 15 mya. Interestingly the youngest and largest island in the group, Hawai'i, formed only 400,000 ya! Located on an active volcanic hotspot has meant that the older and smaller islands of the HI (located to the northwest of the chain) are gradually destroyed as the Pacific continental plate is subducted under the Eurasian plate.

While some of the honeycreepers have the finch-like bill of their ancestors (Chloridops, Ciridops, Loxioides, Melamprosops, Rhodacanthus, Telespiza), largely for cracking seeds, the bills of other species have adapted in a wide display of shapes and sizes. Short sharp bills are consistent with insectivorous species (Aidemedia, Loxops, Oreomystis, Paroreomyza, Xestospiza), but also may also be used in gathering nectar. Long curved upper bills combined with a shorter mandible were useful for digging out insects from branches (Hemignathus). Specialist nectarivorous birds have longer thinner bills for probing flowers (Akialoa, Drepanis, Himatione; see also Sugar Hit 1 - Nectarivorous birds and Sugar Hit 2 - Beak Comparison Nectivorous Birds ). Hooked bill species were odd specialists: Dysmorodrepanis (pincer beak for fruit and snails), Psittirostra (fruit) and Pseudonestor (probing wood for insect larvae). In all, the Hawaiian honeycreepers consist of 24 genera with 57 named species. However they could be a poster child for Holocene extinctions with 22 species (and an additional subspecies) having died out during historic times, plus another 18 species are known only from prehistoric subfossil remains. This leaves barely 17 species, less than a third of the group, alive today. Many of these species are severely threatened and could follow the others without concerted conservation efforts. In addition to the previously mentioned threats, avian malaria spread by non-native mosquitoes continues to have a devastating affect on the populations of many species.

Illustrative note: Unless obvious from the name, the abbreviations for the islands are: H - Hawai'i, M - Maui, Mk - Moloka'i, O - O'ahu, K - Kaua'i.

Description

A selection of recently extinct fauna from the Hawaiian Islands, to scale.

Although politically part of the USA, the Hawaiian Islands (HI) are an archipelago of 8 main islands and many smaller ones, situated in the North Pacific over 3600 kms from the North American continent. Volcanic in origin, the environments on the islands varies considerably between tropical lowland and cool alpine on the peaks. Due to their isolation, very few animal groups were able to colonise the islands and consequently there is a high degree of endemism in the fauna and flora.

As with many of the remote island groups in the Pacific, humans were very late in colonising the HI. Polynesians first made landfall sometime between 124 and 1120 AD, while the first Europeans didn't arrive until 1542 (Spanish explorers). It was only following the 1778 visit by British explorer Captain James Cook that Europeans finally established colonies on the islands. As usual human contact brought an immediate impact with habitat clearing and the introduction (deliberate/accidental) of a wide array of pest species. In addition many species were hunted in large numbers as specimens for the amateur/museum collection trade. Many native birds were flightless or naive towards predators, and as a result the HI has experienced one of the highest extinction rates globally. There will be several posts to cover the extinct vertebrate fauna (mostly birds) of the HI; this one will focus on the endemic Hawaiian honeycreepers.

Quite feasibly, the honeycreepers of the HI represent the most impressive example of adaptive radiation among vertebrates. Despite the name, they were not closely related to the true Neotropical Cyanerpes honeycreepers which are specialised tanagers (Thraupidae). However prior to molecular studies, it was uncertain as where the origins of Hawaiian honeycreepers lay. Previously they had been placed in their own family ('Drepanidae'), linked to the American sparrows/buntings, and finally are now considered a very specialised branch of the cardueline finches within the Fringillidae or true finches. The honeycreepers split from their closest living relatives, the Eurasian rosefinches, between 7 and 15 mya. Interestingly the youngest and largest island in the group, Hawai'i, formed only 400,000 ya! Located on an active volcanic hotspot has meant that the older and smaller islands of the HI (located to the northwest of the chain) are gradually destroyed as the Pacific continental plate is subducted under the Eurasian plate.

While some of the honeycreepers have the finch-like bill of their ancestors (Chloridops, Ciridops, Loxioides, Melamprosops, Rhodacanthus, Telespiza), largely for cracking seeds, the bills of other species have adapted in a wide display of shapes and sizes. Short sharp bills are consistent with insectivorous species (Aidemedia, Loxops, Oreomystis, Paroreomyza, Xestospiza), but also may also be used in gathering nectar. Long curved upper bills combined with a shorter mandible were useful for digging out insects from branches (Hemignathus). Specialist nectarivorous birds have longer thinner bills for probing flowers (Akialoa, Drepanis, Himatione; see also Sugar Hit 1 - Nectarivorous birds and Sugar Hit 2 - Beak Comparison Nectivorous Birds ). Hooked bill species were odd specialists: Dysmorodrepanis (pincer beak for fruit and snails), Psittirostra (fruit) and Pseudonestor (probing wood for insect larvae). In all, the Hawaiian honeycreepers consist of 24 genera with 57 named species. However they could be a poster child for Holocene extinctions with 22 species (and an additional subspecies) having died out during historic times, plus another 18 species are known only from prehistoric subfossil remains. This leaves barely 17 species, less than a third of the group, alive today. Many of these species are severely threatened and could follow the others without concerted conservation efforts. In addition to the previously mentioned threats, avian malaria spread by non-native mosquitoes continues to have a devastating affect on the populations of many species.

Illustrative note: Unless obvious from the name, the abbreviations for the islands are: H - Hawai'i, M - Maui, Mk - Moloka'i, O - O'ahu, K - Kaua'i.