Not neonatology: Adaptive Variation in the Hawaiian Honeycreepers

The break in my posts was partly due to a vacation in Hawaii, where I was fortunate to have some time to go birding, and take some photographs of birds from a group that has a remarkable evolutionary history, but which is much less well known than Darwin’s Finches. The Hawaiian Honeycreepers are now known to have diverged from a common ancestor. They are all now endangered, critically endangered or extinct, but those that I was able to see are beautiful unique birds.

Above is one of the least endangered, the Apapani, shown here in an Ohia tree, with its curved beak adapted to seeking nectar from the flowers of this tree.

The I’iwi is an iconic bird, shown on Hawaiian publicities or posters whenever they want a photo of a bird

It has somehow learnt to puncture the nectaries of invasive plant species, like the poka banana that this individual is perched on.

These birds are threatened by the loss of habitat, especially the loss of the Ohia tree which is being attacked by ROD (Rapid Ohia Death) due to a fungus probably brought in by the nursery tree industry. They also lack immunity to two mosquito transmitted diseases, avian pox and avian malaria. Mosquitoes were absent on these islands until recently, and the birds have no immunity to the disease carried by them. Each year, with climate warming, the mosquitoes are found at higher and higher altitude, and the birds retreat to smaller and smaller regions of Hawaii.

The Akiapola’au is a bird with a remarkable beak, but only about 600 are left, it is dependent on the Koa tree.

The lower bill is used like a woodpecker to tap and make holes in tree bark, and the long curved upper bill then probes to remove beetle larvae. It is an exclusive insectivore, unlike the other Honeycreepers.

The even more endangered Palila is only found in dry Mamane forest on the western slopes of Mauna Kea above 2000 m elevation. The remaining range is about 5% of its recent extent. It has evolved a resistance to the toxic phenols in the seeds of the Mamane, which is a leguminous flowering tree under threat from invasive species. Most other small animals find the Mamane seeds and pods toxic.

Not the best photo, but there are so few of these birds left I find myself fortunate to have seen one perched among the flowers of the Mamane. The are also very smart birds, as they were able to take the Hawaiian Department of Land and Natural Resources to court and win, to force them to provide some protection of their habitat. : Palila v. Hawaii Department of Land and Natural Resources, 852 F.2d 1106 (9th Cir, 1988).

The evolutionary history and relationships of these birds has been clarified in the recent past and correlated with the appearance of the larger Hawaiian Islands, (Heather R.L. Lerner, et al. Multilocus Resolution of Phylogeny and Timescale in the Extant Adaptive Radiation of Hawaiian Honeycreepers, Current Biology, 2011 (21) 1838-1844).

Bayesian Divergence Date Estimates for Hawaiian Honeycreepers from Whole Mitochondrial Genomes Based on Three Island Age Calibration Points
Mean ages are shown above each node, with horizontal bars across nodes representing 95% highest probability density intervals. Shaded vertical bars encompass the estimated subaerial to maximal shield-building dates for the recent Hawaiian Islands, where the gray bars indicate island ages used as calibrations, and asterisks () identify constrained nodes. Lowercase letters identify divergence of a new morphological lineage before formation of Oahu (a), during or after formation of Oahu (b), or before or during formation of Maui Nui (c). Distributions by island are listed to the right of each taxon where closed circles denote historic and/or extant (and sometimes fossil) distributions, and open circles represent fossil distributions with no known historic or extant populations. (1) The extant population occurs on Nihoa Island, but closely related extinct species mainly differing in size occurred on Kauai, Oahu, and Hawaii Islands. (2) The extant population occurs on Laysan Island, but closely related extinct species mainly differing in sizes occurred on Kauai and Hawaii Islands. (3) A closely related species or subspecies occurred on Laysan Island. Photographs are by Jack Jeffrey

They appear to have arrived after Kauai was formed, then cooled, then was colonized by plants, about 5.8 million years ago, with their forefathers being Eurasian Rosefinches. Each successive island has been colonized and then the various ecological niches been filled by adaptive radiation. Visiting the Hakalau Forest Natural Wildlife Reserve on Hawaii, where I photographed the I’iwi and the Akiapola’au was a highlight, special access with an approved guide is required, and we were fortunate to be able to go with Jack Jeffrey, who took the photos included in that figure above.

I put a few more of my photos of birds from Hawaii on a new page of the blog.

Personally I find the birds more impressive than Darwin’s Finches (which are not actually finches but Tanagers), the Honeycreepers in contrast are actually Finches, but have dramatically varying beaks and coloration, despite their common ancestry. Perhaps if they were more famous, and someone wrote a successful book about them, we might be able to stop their decline and prevent their disappearance.

About Keith Barrington

I am a neonatologist and clinical researcher at Sainte Justine University Health Center in Montréal
This entry was posted in Not neonatology. Bookmark the permalink.

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.